Halo

On the first level, when you meet the captain and he gives you a pistol, go up to the point where you have ammo for your pistol. As soon as you have ammo for it, turn around and go back to the captain. Kill him with your pistol and then you will here Cortana say "What the hell do you think you are doing?! Attention Marines, the Master Chief has gone rampant, let's bring him down boys." Then, swarms of marines will come after you trying to kill you. You can use this to practise your skills if you wish as no matter how many marines you kill, they just keep coming.

In the later levels of the game you will encounter new enemies called Flugs. These enemies will be small at first, but they will attack and control anything alive. Use a shotgun on these baby Flug as they tend to group in large numbers. By using the shotgun it will send a storm of bullets and kill most of them that are around. Use a shotgun on the possessed Flug, and it will kill most of them in one shot. This is made easier by the fact that most of them carry shotguns.

When the Grunts are sleeping you can beat them to death with the butt of your gun without waking up any of the other Grunts. You can usually kill a four to seven of them before an alien spots you. They start sleeping in level 5, Assault on the Control Room. Just remember not to shoot or they will wake up.

Use a photon weapon to destroy a Jackel's shield quickly. When you encounter a Jackel, run up and hit it with your weapon or get out a gun that uses bullets, not energy.

To defeat the second level on Halo easily, the one where you have to kill all the aliens and rescue the survivors, kill the survivors instead. It's much easier and quicker then.

This is more of a technique than a cheat. It helps you to kill elites. Heres how you do it: First, you need a plasma pistol and a human pistol. When you have those, use the plasma pistol first. Charge it up completely. Once charged, shoot the elite anywhere with the fully charged plasma bolt (taking off his shield). After that quickly take out your human pistol and shoot the elite in the head. Note, this will kill any elite instantly if done right. If you don't shoot his head, it only takes a few body shots.

Covenant:

Grunts: Any weapon.

Jackals: Human pistol.

Elites: Plasma weapons/assault rifle/sniper rifles/rocket launchers.

Hunters: Rocket launches/grenades/assault rifles.

Flood:

Little dudes (parasites): Assault rifles.

Cadavers (body’s): Shotgun.

Exploding things: Nothing can stop them from exploding.

When you run into a hunter, pull out the human pistol. As it charges at you, it will lift its gun arm, revieling a spot of orange flesh. Shoot there. This Also works in the centre of the back and in the back and side of the neck. All these places will kill the hunter in one shot.

This one works with all of the flood exept the little spider ones. Grab plasma weapons exept for the needlers. Shoot the plasma weapons at them and the flood will fall down and keep shooting them until there is blood all around them. For the covenant, shoot the plasma weapons at them. If you shoot elites, it only should take a few shots to wear down their energy shield with Plasma weapons, then shoot them 3 more times and they'll die. It should only take 2 shots at the most for grunts. The jackals have sheild but you can wear them down with plasma weapons and 2 shots to kill them. You have to switch excessively because the battery runs low. Finding plasma weapons shouldn't be a problem because the Flood and the Covenant carry them all throughout the game.

Play levels your stuck on in co-op and have one player always hang back in a safe place. This way the other player keeps charging in and killing things. Because one player is far back you'll be able to respawn unlimited times and take out large armies bit by bit.