Assault
Attackers
Assault is a type of reverse CTF in which one team must ferry the bomb from their start point into the enemies base and then man it. Assault can be a very difficult gametype since most of the enemy tends to camp inside or around the base so there is usually no way in. The spiker grenade, the power drainer, and radar jammer in combination or even seperately are very effective at emptying out bases and in Assault they can be very useful in giving you time to arm the bomb. If you use the power drainer on the enemy base remember you can't go in there until the effect is over because it will kill your team too. The radar jammer is a better alternative to the power drainer in that it will confuse the enemy and give your team a chance to plant the bomb. However going into the radar jammers sphere of influence without a plan can cause your team to become just as disorganized as your opponent. The most simple cut and dry tactic to empty the base is to pepper it with grenades; frag and spike grenades are most favorable. Also very effective at clearing out the base is the Spartan Laser, Missile Pod, and Rocket Launcher.
Defenders
Defending the base is just as important as attacking it since Assault rotates between attack and defend. On a large map it can be very beneficial for the defending team to control the vehicles as they can cause mayhem to the on foot attackers. However the defenders have to be very careful because a well placed missile/rocket can annihilate all but the Wraith and Scorpion in a single shot. When defending the base the bubble shield is a definite must-have for the defenders but it is inadvisable to put it directly over the bomb arming point because it could make it a lot harder to kill the attacker. Usually putting it at a choke point inside the base such as a small hallway where you can pop in and out of the shield can be very benefical to defense. The one drawback to this is if the attackers kill all the defenders the bubble shield can give them a safe location to rally inside your base.

Juggernaut
Juggernaut
When playing as the juggernaut one of the best strategies is always to collect the power weapons and have a good balance between short and long range weapons since both come in handy. Usually however the juggernaut uses short range weapons more due to the speed and constant movement that the juggernaut has to do to keep from being killed. One of the main things the juggernaut has to look out for is plasma grenades because they can significantly lower the juggernauts shields which will make you vulnerable to weaker arms fire. A smart group of attackers will usually group together to take out the Juggernaut but their are always those that trail off and think they can take the juggernaut by themselves. These are the type of people you want to target as they'll be the easiest kills. Trying to take on a group of attackers can be done successfully providing you have the right weapons but the lack of guarantee in the success of the fight makes taking on the group a inadvisable strategy.
Not Juggernaut
When your not playing as the juggernaut you want to become the juggernaut because only the juggernaut can win the game. The best ways to become the juggernaut is to team up with the other players and take the juggernaut on at once. Unfortunately the obvious drawback to this is as soon as you become the juggernaut you'll be the new target of everyone else and since they'll be all around you, you most likely won't last long. One of the best ways to take out the juggernaut is to carry the heavy weapon and plasma grenades. Also a sure fire way of killing the juggernaut is to melee them in the back. If you choose to seek out the juggernaut by yourself the best way to handle the encounter is to stay at a medium distance and strafe around the juggernaut randomly changing directions. Also if there is multi-levels to the map to elevate yourself and jump down; the main objective of these seemingly random movements is to get behind the juggernaut and perform a melee to the back. This will instantly kill even the overshielded juggernaut and since you were by yourself when this occured you won't have to worry about being instantly killed by your former teammates, at least for a few moments.

King of the Hill
One of the main parts of King of the Hill is obviously the hill. This is represented by semi transparent circle which may or may not rotate based on the sub-gametype. This new semi transparency makes it more difficult to see who's in the hill and what they are armed with. This means when your going to take control of the hill its best to go in heavily armed. (Just be careful not to blow yourself up.) Grenades are the most common method of emptying the hill and there is usually at least one grenade in the hill exploding at any one time it is occupied. The most ingenious way to offset heavy arms fire and grenades is to place a bubble shield inside the hill which deflects all fire. The only drawback to the bubble shield is that to defend the hill you have to pop outside of the bubble shield or your teammates have to fight to the death to get the maximum amount of time possible. In trying to capture the hill a enemy could use the Radar Jammer or the Power Drainer either one could severely disorient and even kill the opposing team. Using these power-ups is extremely effective since the other equipment (i.e. power drainer, radar jammer) goes through the bubble shield so the shield cannot protect them.

Capture the Flag
In many respects CTF is like assault except instead of having he flag to start out with and infiltrating the enemies based to plant it you have to capture the flag and escort it back to your base. This can be made exceedingly complicated with settings like flag reset on touch.

Offense
The main strategy used when playing offense on capture the flag is to rush the enemy base blindly from all entrances overwhelming them and causing them to respawn further way from the base so your team, or what's left of it gets the flag out of the base then dies on the way back. This strategy is good except for the few major flaws it has. Before blindly rushing the base remember to collect the power weapons along the way, going up against 4 or so enemies is much easier with a rocket launcher than with a assault rifle. Next take a few seconds to do reconnaissance. This may give the opposing team a second or more to get organized but it'll also give you valuable information as to where your enemy is and what they are armed with. Reconnaissance is most useful when your watching your enemy stealthily and not being watched yourself. Maintaining the element of surprise is often the best bet to beat your enemy even if slightly out gunned. Once the attack has penetrated into the base and the flag is in sight don't just make a bad dash for the flag. Firstly, you have to watch out for trip mines, power drainers, or other things that might kill you. The best bet if you actually want to be the flag carrier and survive is to let someone else get the flag first and get it off the pedestal and when he is attacked and killed by the enemy finish, jump in and finish off the enemy and take the flag from there. Traveling the road less traveled is a good philosophy, especially so in CTF. You won't get far trying to take the flag through the middle of a firefight, because the enemy team usually directs all their fire at you. Also if you get stuck in a one on one encounter with a brave enemy that wanders out of the base, don't be afraid to drop the flag (out of reach of the enemy) and go mono a mono with the enemy. Just remember with the flag reset on if the enemy even touches the flag it'll vanish from the battle and all that progress will be lost so don't make it easy for them.
Trying a vehicular approach can sometimes work and in the case of the warthog can get 3 teammates to the base at once to provide more firepower but at the same time your painting yourself as quite a large target for the initial wave of rocket and spartan laser fire. Vehicles in CTF have a much higher calling as transportation for the flag carrier than attack platforms as vehicles like the Warthog and Mongoose have excellent carrier capacity and are fast and agile. For a quick entry the Banshee drop into the base is still a excellent strategy. Speed boost across the entire level completely ignoring anyone that tries to shot you (except rockets of course, dodge those) and once your over the enemy base get out of the banshee and just let the banshee fall away. You won't need it since you can't transport the flag in it. If your a skilled banshee dropper you can land right on top of the base and drop down into the base or go through a side entrance, depending on what map your playing. This strategy can be brutally effective if you have a warthog or mongoose waiting for you somewhere near by. To do this requires a lot of team coordination but the other team usually won't know what hit them.
Defense
In games like CTF and even Assault defending the base is one of the most under-appreciated roles on a team. Nobody wants to do it because they have to stay in one place and wait for the enemy to come to them. This mind-set is especially prevalent when the team is in the lead. If you are losing in a objective based game chances are the leading team is all coming after you and have over confidently left there base defenseless. This can be used to your advantage if you are able to escape the enemies sights. Even once you have the objective and the enemy is alerted, often times they continue to just beat down your team as they spawn not realizing they're about to lose a point. If you cannot get passed the enemy your team can do best by laying low inside the base and taking on attackers one at a time. This strategy however can't last forever because once the enemy has a commanding presence in the base the game will spawn you away from the base in a attempt to keep you from being spawn killed.
The most basic but effective techniques to defend the base including keeping the vehicles at the base and hording the power weapons. When a enemy comes to you you can just blow them away with a rocket launcher, especially on a big map when they'll most likely be coming by vehicle. Variations of this that might be a little more complex and require a little more team coordination involve stationing people around and outside your base and at halfway points along the map's border. This will thin down the enemies numbers as they approach your base and if done correctly has the potential to quarantine the enemy within a certain area keeping the flag well out of reach. The drawback to this is of course if your not by the base then you don't know if the enemy has slipped base you either. No matter what strategy you use its always a good idea to keep at least 1 or 2 people stationed in the base right next to the flag (out of direct fire though) so you can keep a eye on it. This position which is the most defensive you can possibly be on CTF is one that some people like but most people don't. But nonetheless it is essential if you want to last more than a few minutes.

Oddball
With the oddball you have pretty much 2 choices. Find the oddball and hide in a "safe" spot. Or run around and hope you don't get caught by the group of people looking for you. Choice one is often the better of the two choices but has its fatal flaw in that there are no 100% safe spots and where ever you go someone is going to find you eventually. If its just one person you can melee kill them or drop the oddball and kill them with whatever weapon your wielding preferably a power weapon such as a shotgun for short range or a rocket launcher/missile pod for longer range. The oddball is a one hit melee kill so if it is just one person try and use this melee to keep them the enemy off your back. The second choice is a little more difficult but can be more effective if done correctly. Running around with the oddball can prove one of the most useful methods of keeping it as nobody can gang up on a specific spot to flush you out and you have less chance of being nailed by a grenade. The main flaw with running around is that eventually you'll accumulate a group that is trailing you of multiple people and if they catch up the conflict is almost always over fast. Until of course the next person picks up the ball. Whichever method you decide to use you should always keep in mind some other tips. If you know someone is tailing you and they're hitting you in the back with say a Battle Rifle; you can step around the corner and as soon as they come through the doorway crouch down and melee them with oddball. You can do that about once or twice before people catch on and start throwing grenades. Equipment is usually not very effective with oddball because its such as fast paced gametype and usually moves around but on team oddball the bubble shield can come in handy if your team can defend one position.

Slayer
Slayer is the most basic and played gametype in all of Halo. Its the default killing action that we've all come to know and enjoy. As such there really isn't a lot to say about the gametype because it doesn't specialize in anything and is just killing to gain as many kills as possible to win. The best ideas for this gametype are to control the power weapons and not to die. The "not dying" part is usually harder than acquiring the power weapons but it is possible if you play your cards right and pick your battles. Unfortunately most people don't pick there battles since this gametype relies solely on the number of kills, most people just charge blindly into a conflict hoping to get a kill and completely disregarding the fact that if they lose they've just provide someone else with a kill point.

Territories
In territories there are offensive and defensive rounds, and five Territories throughout the level during each round. One team must defend the Territories from being captured, while the other tries to capture as many as they can per round. Once the territory is captured it cannot be taken back. The best way to proceed with these games is to get the entire team to focus on one or two territories depending on the size of the team. Of course the enemy will know you are doing this and they will focus there strength on defending these. The one disadvantage to the team trying to take the territory is they have to stand in the territory to capture it which allows the enemy, who doesn't, to just chuck grenades at the territory killing all the attackers. However, the bubble shield can easily compensate for that and will force the enemy to fight at much closer range. Good weapons to carry for the attacker are the shotgun and battle rifle/assault rifle or something heavier like the missile pod/rocket launcher and of course the bubble shield. Good weapons for the defenders of the territories are the power drainer, sniper rifle, rocket launcher, missile pod, and machine gun turret.
Great technique for fooling the enemy into giving up one or even two territories is to focus all your strength except one or two teammates onto a single base and continually assault the base but don't actually take it...yet. 9 times out of 10 this will fool the enemy into thinking your assaulting one base at a time and your other teammates that aren't in the skirmish can sneak away and take at least two territories before the enemy catches on to the idea. If they do catch on then they might draw away some of the forces from the main assaulted territory, which with most of your guys fighting at should be a easy one to capture if the enemy reduces its strength. Beware though, it only takes one spike grenade in close proximity to empty a territory out and lose the capture.

VIP
When playing VIP games the player who gets VIP either has to hang back and be well defended or has to go on the offensive and get the other person. The overshield that the VIP receives makes them invaluable to the team in taking down the other VIP but going on the offensive can put the VIP in a lot of risk if the teammates aren't looking out for him. However staying on the defensive can allow your enemy team to pick up all the power weapons and then its pretty much impossible to turn the tide of battle. The disadvantages of going on the offensive can be counter by good planning. If the VIP loses his overshield then its best to withdraw from the situation and having a good escape route from where ever you go is essential for keeping the VIP alive. Remember your deaths and kills don't matter unless it involves the enemy VIP so don't be afraid to take one for the team and step in front of a enemy to shield the VIP if they're low. If your team wants to be super defensive and force the other team to come to you then the best bet is to have the VIP stand in a bubble shield and defend that area with everything you have. Of course this means that you'll usually be overwhelmed eventually but if you can draw out the enemy VIP it'll be a easy kill for your team. Unfortunately with this super defense the enemy team is usually smart enough not to send the VIP over; unless they come over against the wishes of their team.

Infection
Not much is known about the Infection gametype including its legitimacy as being included into the actual game but as it is now the gametype is basically fighting flood infection, combat, and carrier forms which presumably spawn in large amounts and are never ending. A gametype like this would most likely be carried out as a sort of last man standing game with the last person not being infected by the flood and presumably out of the round winning.