Ammunition
Guns and ammunition will also be encountered in each level. When you find ammunition for a gun you do not possess, it usually indicates that the new weapon is also hidden somewhere on the current level. You will usually find more ammunition of a certain type that is most useful in the current level.
Cover
When encountering enemies, take a look around for things that you can use for cover. Select the appropriate weapon and try to shoot them at a distance before you are spotted. Then, use walls or objects as cover.
