There is a concept of 'threat levels'. You get more points for killing people who are more threatening than you. So if you are on foot, and your enemy is in a tank, they are a bigger threat. If they have a higher K/D than you, then they are a bigger threat too. There's also bonus points for squad leader and commander.
At the end of the round, you may get some bonus points. How many depends on your final K/D. If you finish with 20/0 you will get much higher end bonus than if you finish 20/12.
