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 looks for you. Many of the newer first player games allow the sun to be used as it would in real life. So going up a hill and having the sun at your back will give you a natural advantage in the game, and allow you to snipe from the same spot for a longer time before someone finds and kills you.
Another way to get a higher score is to work as a team with other players. Most people playing a First Player Shooter are playing alone with the goal of running around and killing everything that moves, but if you and some friends are playing you can use each other as in real combat. Now that you have other people watching your back as a unit you can be a more effective killer in the game, an example of this is that in some of the delta force games you can take a helicopter and if your friend is flying it you and another friend can man the chain guns and you can cover a bigger area, and deciding on a plan before starting the game you can develop a good strategy as a professional gambler or Online Poker player would allowing you to focus on 1 thing instead of many different aspects of the game.
Many times I would jump into the pilots chair and other players would jump in and I would circle the enemy camp but the players in the back of my chopper would not attack instead they would jump out or just wait for me to land instead of helping me attack from the air. So instead of increasing our chances of winning by working together they just wanted to be a team of 1. This will decrease the chances of our team winning the game, just like a player at a blackjack table can make all the other players lose by making bad decisions when it is that players turn.
Formulating a good strategy, playing as a team and using all available tools at your disposal you can not only win more games and get more points, you will also have a better online gaming experience, and this applies to playing first person shooter games and gambling in online casinos.