fps help

I am a pretty proud gamer but after being beaten heavily in halo and now failing in the resistance demo, i realize i'm quite a fps noob. referring specifically to the resistance demo. It starts with me behind a wall, I shoot at them from the corner of the wall but nothing happens, so i run towards them until the aim turns red, before i can start shooting, i'm dead., can u guys give me any fps advice in general? any referring specifically for resistance.

if it helps ur analysis in any way, I own in third person shooters (RE4, Uncharted)

1. Use cover. If you don't have a good spot look for a hiding spot before you run out.

2. Make sure you can move. Sometimes you may be stuck behind a small area of cover and not able to move because you will get shot.

3. If there are WAY more then you use gernades. Some forget they have them.

4. Know how many there are. If there are a ton in one area you need to know.