Avoiding Enemy FireDo not run out in the open. 9 times out of 10 you will be shot down. I'm not suggesting you camp, but find some reasonable cover or an area where you aren't vulnerable.
Height is a huge advantage.
One thing I tend to do a lot is the
drop-shot. If you are in a bit of a duel with someone, go prone as you are shooting and you will find a lot of the bullets will go flying over your head.
In Halo, the common thing to do is strafing, where you move around to avoid bullets. While this is not so common in tactical games like COD4, it still works, particularly if someone is sniping at you. It is much easier to hit a stationary target than one that is moving around.
Learn The Maps You will only do this by playing and watching others. Learn where common spots are, where people are likely to be. Learn how to get to a certain area without being noticed by the opposition.
Perks / AttachmentsIf you want to improve, my advice is to avoid using these perks: Juggernaut, Martydom, RPG, 3 Frags, Last Stand.
If you are playing in a Softcore server, almost always use
Stopping Power. It adds a huge advantage (as I believe Col Walker said, 140% increase on damage). If you are playing Hardcore, I would suggest
UAV Jammer or
Sleight of Hand.
Bandolier is always a bonus, especially if you are capable of surviving for long periods of time.
For the third perk, Dead Silence is pretty much a must. Otherwise,
Iron Lungs for Snipers, or Deep Impact and Steady Aim for other guns (SA particularly for close range weapons).
For the other attachments, it really depends on the gun.
SMGs go together very well with silencers. As they are typically close range weapons, and the silencer decreases range, it has no huge negative effect.
ARs are really at the discretion of the user. Most of them have good iron sights and don't require an RDS or ACOG, so silencer is an option. But as ARs are often used long range, it is probably not a good idea. All I can say is
experiment and find out what works for you. Getting used to a particular attachment (or an absence of one) will improve your game.
The DeagleAt close range, the Deagle is a great asset to have.
If you have one, use it. Learn how to use it. Watch others who use it. When using it at close range, you don't necessarily have to aim down the sights. The crosshairs are sufficient.
Just fire that thing as fast as possible! It is very high damage (especially with stopping power) and will often beat close range guns such as SMGs and sometimes shotguns.
That's all I can really think of right now. As they say, practise makes perfect. Some of these views may seem a bit strong but these are just my personal recommendation if you are wanting to improve.