Well lucky for you I just finished my routine playing of Halo 4.
Infinite Slayer is quite different from the Slayers of Halo because you have loadouts and receive an ordnance drop for gaining points by killing the enemy team. It's quite easy to gain the upper-hand by calling down a power-weapon, such as a shotgun, or even a couple of grenades to clear out an area. Try out all the perks, they're called tactical/suppourt packages, to see which one suits your play style. Same goes with the Armour Abilities. Personally I use Firepower, lets me use a primary weapon in my secondary weapon slot, and Dexterity which decreases the time it takes to reload and swap weapons. My armour ability of choice is Promethean Vision, looking through walls and terrain to see where the enemy is, because knowledge is power. It's great to use when you have a weapon, such as the boltshot, and you can time it when they come out.
Speaking of the boltshot, it's a secondary weapon which is mostly used for corner kills. It's a one-shot kill so don't rush around corners, give yourself some space. This is common sense for shooters but moreso because everyone can wield it, i.e. it's not a power weapon. I should also note there are no medkits so your shield is your life. Why they took out health bars I really have no idea. The health system was great before but *shrug.*
SWAT is good practice for aiming but it won't translate very well over into other game-modes because you get no shields in SWAT so a headshot is an instant kill. In other game modes, a headshot is not an instant kill. Just something I realized when I thought, "Hey, this will help me with my DMR aming."
Now I'm going to stop here because I've already rambled on too much xD.
EDIT: Trupoluv reminded me of another big aspect. Never wander off by yourself unless you're sure the enemy isn't around or your team-mates are close by. This is because team-playing will make the difference between victory and defeat. Even if you can't go around in a 4-man team, stick with someone else. Pick off the enemy one by one when you can and the game should be significantly easier.
