Middle game (assuming an average stack, meaning you have roughly 15-20 times the BB), stop playing low pocket pairs unless you're in late position and there's only one person in the pot with you (in this situation, raise).

Don't draw in the middle game. Don't play drawing hands (unless you're in a good spot to raise a fairly uncontested pot).

Reading things on here, you'll start to pick up on patterns of what people have when they make various plays. HOH2 talks about a few of these as well. Beyond that, the best teacher is experience.

From your post, I'm thinking that your biggest hangup is a lack of aggression. Once the game gets to the point that the pots are meaningful, you have to start upping your aggression (both when you have hands and when you don't). You should ALWAYS be raising much more often than you're calling. I honestly believe that a player can have success if they eliminate calling from their book of plays unless it's a very specific situation.