Can't help with halo but for COD4 i can, when you shoot someone always follow them down because tons of people have the last stand perk (like me) and they will pop you off if you don't pay attention lol, also if they have the martyrdom perk they will drop a live grenade so dont bother running in. Never bother trying to throw a grenade back that has been thrown at you because i would say 90% of the online population cook their grenades, which is also a good thing to do just hold whatever button you use to throw your grenade down and then throw it this way it will detonate earlier and so theres less chance of people sprinting away from it. Don't Spray everywhere as well as being a really nooby thing to do you will run out of ammo and then all youve got is your pistol and your knife which can still pull of a few kills but i would rather have some sort of semi-automatic on my side lol. If all else fails then go prone its very nooby but sometimes its just what you need. If you are going to camp, say you are a sniper then after youve killed someone move to a different postition because they will run in for you afterwards. When you unlock the claymore perk then you can put these at entrances so enemies cant rush in and stab you before you know it, claymore are also usefull when placed in tall grass because the enemy has no idea its there, i can't really think of much more the more you play the better you will get lol.
