I've gotten to the stage where I'm an OK laner at the start of the game - unless things go terribly wrong, I can stick around and keep up in levels. However, when the mid game is reached, I tend to fall behind and start feeding a fair amount. What should I be doing mid game?
Really it just takes alot of experience to get good at this game. Midgame you need to be ganking and watching for ganks. Coordinate with your teammates, use wards, etc. Hang in there and you'll eventually get better.