I've discovered that against my two main opponents (my old man and the chess program on OSX) I play best when there are lots of pieces on the board. Especialy when there are lots of pawns. Are there any specific tactics that will stop my opponent accepting pawn exchanges as I move my pawns up the board?
Well, for one, you could simply not make many pawn moves. This will lead to limited exchanges, but also a very cramped position for you.
Another strategy is to have a spot prepared so you can move your pawn up a square when it's attacked. If you want to avoid the exchange, you can just move the pawn. However, this'll lead to a hyperextended pawn chain, that'll eventually be traded off if your opponent knows that he should.
Both of those methods work, but only superficially. If your opponent knows what he's doing, he'll exploit either of the two weaknesses. Therefore, my best suggestion is to play an opening that's know as closed. I need others to help me out on this, but I believe the Roy Lopez leads to very few exchanges.