Good Pincushions:
When in possession of the alien Needler, you can do some devastating damage. To maximize its effectiveness you should be a stone's throw away from your target. Make sure as many needles hit your assailant as possible. Since they explode shortly after impact, you can cause an awesome chain reaction that is quite explosive to the now charred enemy and anything else in close proximity to your victim.

Left Wide Open:
If you're looking to to knock out the round shield wielded by the mid-sized aliens, then grab one of their weapons and hold the fire button down for a shot to charge. Now let it rip! It will permanently disable the bastard's shield, leaving him completely wide open.

Toro! Toro!:
Don't back down from those huge mortar toting Hunters. Yes, they are massive, and yes they are pretty darn hard to kill. But this is what you do.Grab a few of those adhesive plasma grenades from fallen foes. When a hunter charges you, run backwards facing the brute and toss a few plasma grenades on the sucker. You need good aim. The adhesive grenades will stick to the Hunter leaving no way to remove them other than the inevitable explosion. BOOM! Or... Hunters can be pretty damn annoying, but not to me. If you can get a hunter you swing his shield at you, then when he's swinging, strafe around to get behind him, and shoot him ONCE in that squishy orange stuff in his back. If you hit him right, 1 shot will kill him. 1 bullet, to kill a hunter. Easy stuff.

Pistol-Whip It Good:
Never underestimate the power of a well-placed melee attack. Smacking someone or something with the butt of your gun is great fun and immensely effective.

Bomb Onboard:
Don't hesitate to stick a plasma grenade to any vehicle in the game. Sabotage is great!

Board Them:
In thge very beginning of the game when you are trying to escape the Pillar of Autumn, you can find cloak devices and Overshields (shields that double over your existing shield). When you locate the area where the escape pods are, you should find a couple Covenant boarding pods. This is how they have boarded your ship through your empty escape pod airlocks. Within their boarding pods you should find a few handy items.

Best Anti-Flood Weapon:
The combat shotgun is the best weapon when you fight the flood. It'll take them dow nin 1 or 2 shots.Forget the assault rifle or the plasma weapons shotgun is the way to go.

Overshields Over There:
In the level "The Silent Cartographer" where you disable the security systems, theres three overshields near a couple of those purple barrel things. When you're about to enter the first hallway into the security disabling room, before you even go in the structure, turn left and there should be some purple container/barrel things, with three overshields littered around them. Have fun!

Banshees & Shortcuts:
In the level where you charge the control room, the snow one, you can hi-jack an enemy banshee. When your in the corridor and it says "If I had a Super Weapon" in the bottom right hand side, you can snipe down the covenant that will get into the banshee. If you do snipe him down, make a break for the banshee and hop in. Even if you don't get the Banshee, you can still skip half the level by turning left as soon as you come out of the door and falling off the bridge. The wall will break your fall, so you don't get hurt, from there you can head up to the control room and beat the level in no time.

Get the Drop on the Dropship:
When a drop ship unloads aliens, the next drop ship will hover in the air. If you take your sniper rifle and zoom in on the sides where the doors open, the targeting cursor will turn red. Fire once or twice and the alien will plummet to the ground.