Just keep playing. It's the only proven way to get better

Ignore the whiners, complainers, and shit-talkers. One way is to find a group of people you enjoy playing with, send them friend requests and stick with them. You can find people out there who aren't total assholes and will accept you regardless of your skill level.

Send me a friend request if you wish my gamertag is meenstreek. I play with people who are pretty good at gears, halo, cod2, etc... However, they don't take the game so seriously as to ruin the enjoyment of others. That for me is the best aspect of Live, which is having fun with people you enjoy.