The way most first player shooters score kills is simple to understand the harder it is to make the kill the more points you get. This means that if you kill someone with a knife you will get more points then someone using a chain gun, but running around with just your knife out is a big gamble unless you are extremely skilled at the game. This method of play will usually just make you the biggest loser.
One way to get a good score is to take a long range weapon like a sniper rifle and camp out near the enemy camps spawn point. By doing this every time someone on the opposing team gets killed they will instantly revert back to the spawn point and you can shoot them, then they will disappear and then reappear and you can shoot them again.
You get fewer points like this, but it is the same principal as playing roulette in the casinos, it is easier to get many smaller wins, rather then one big win.
When using this method try to pick your location using your head and do not just take a gamble on your sniping spot. You will want to have the advantage of height, but sometimes if you can get a good shot and be in a lower location it may be the last place someone...