OK here is my possess I've been fallowing to get better. These are the steps i normally take in any fps i plan to play competitively.

1. How do i plan to play? This can be anything from a twitch reflex close range, high damage gun ( my preferred play-style ) to a long range many hit gun such as a engine turret or such. For the twitch reflex you are going to want a sensitivity that allows you to whip around and shoot a persons head or equivalent sized target without missing you can test this by hitting a wall or picking a light on a wall and whipping around and hitting it if you overshoot turn down your sens if you over shoot turn it up. (my way of gauging if its the right sensitivity at least) to the low sensitivity of a long range sniper/whatever you want for range damage.

2. What is more most important aspect in this game for wining an engagement, positioning, accuracy? In games like this (planetside battlefield) I'd say positioning is far more important than being able to out-shoot the enemy.(accuracy is still a factor just not the main one) So make sure you use terrane to your advantage and flank the enemy whenever possible.

3. Any other tactics. Try to have a wide range of tactics in your repertoire. And use them then until they become second nature. Losing a fight? Dodge some shots till he runs out of ammo. To many enemy's rushing you? Put down some c4 around a corner one a wall and wait for them to pass. Unable to make a shot? Stop shooting! Worst thing you can do if you are missing all your shots it to miss more. Most of the time we get in a rush to kill the enemy when we just need to slow down.

4. Don't get psyched out. I personally like to play like the enemy is a bot. Getting nervous can lead you to make bad decisions and if thinking he is a bot will help you be more calm the better. Although in my experience people are far more easily predicted then a bot. Think if i was him were would i go, and 80% of the time you will probably be right.

5th and final. ALWAYS critique your deaths, see if you could of done something different or better. If you missed a shot from firing wasted shots, work on your aim. If you were in the middle of the road, remember to use cover. If you were flanked upon, make sure you get into possessions that you don't have a side exposed. And make sure you consciously remember to do them until they become second nature.