There are a ton of postings on rank.Do a search for ranking. The short answer is you get more points by chuting, landing and rearming and finishing games.You also can score alot of points in the Zep game.The ranking is done first by rank then by points so someone with a lot less kills can be a lot higher in rank.
Once again...This is a game about flying and tanks and soldiering not who has the most points...Play the game and have fun the points will appear!