Killzone Cheats

Last shots
It should take about four to seven seconds for a grenade to explode. In that time, shoot like crazy. For easier aim (unless they directly in front of you), zoom by pressing R3.

Easy kills
When in possession of either the Helghast assault rifle or the shotgun, conceal yourself near funnel-points for maximum effect. The shot-spread pattern is enough to inflict mortal damage on dense groups of opponents. Should the survivors retreat; chase them with a hand grenade. You can easily knock out entire "clumps" of opponents using only two actions.

When in possession of the sniper rifle, you can take snapshots at "clumps" of enemies. The sniper rifle can eliminate multiple opponents that are "standing-in-line" with a single shot.

Fast gun switching
While sprinting, release the button. As soon as you do that, switch your gun. The next gun will automatically appear in your hands.

Shoot three shells with shotgun
When using the shotgun, it has two modes of fire (regular shoots one shell, alternate shoots two shells). By pressing both fire buttons, you will shoot three shells, which in most cases is more useful. Try using this on groups or stronger enemies.

Multiplayer Tip
When you die, right before you die, throw a grenade, your timing has to be right. You drop the grenade as you die and it will sit there on your body. Five seconds later, when your killer gets ammo from you, he blows up. A nifty trick to get back at the guy who shot you when they search you for ammo.

3 Shots at Once
Grab a shot gun and press the first and secondary fire on it to shoot it 3 times at once, this is perfect for a close-quarter combat online but of course its not effective from far-medium range.