I think generally, apart from just honing your skills and reactions and being that much quicker on the trigger, if you want to keep a better ratio AND play the game as it should be.. stay away from domination game mode
Whenever I have played that, the way to win as a team in most cases is to put your body on the line and not bother about getting killed and push forward as a team. Being the aggressor like that does hurt your kill ratio, but it gets the game won
Of course if you find a server where plenty of other people are willing to do that, you can afford to sit back a bit, defend and pick off the enemy.
My overall suggestion would not to worry too much about your ratio, but find a friendly server where you can get a consistently clean and fun game, where teamwork is used. You'll find the game so much more rewarding, and improve your skills to boot
Sounds like you are a much better player than when you started, so just keep going as you are and in time that ratio will come around without you even worrying about it
