Look into grand prix games. Or any sicilian variations, there are often unusual pawn sacs to witness.
But i'll just give you a few tips.
1. Look for a pawn sac, that wrecks king safety.
2. Look for a good sac, that takes the queen, or any other powerful piece, out of the game for a while, if the piece gets right back into the game next move. It won't logically be worth it.
3. Play gambit openings, they can teach you alot about pawn sacs. Such as Benko gambit, King's gambit, Budapest gambit.
4. Don't get into sac-ing tons of pawns. They can easily be a issue in endgames/no queen games.
This is an area of my game which needs serious developing. I'll look at a game where a GM sacs a pawn either for initiative or piece activity and I'll completely understand the logic of it as I play through the game.
In my own games however, I never see pawn sacs. It just seems to be something I don't consider. I can think of exactly two games where I sacrificed a pawn. In both games the sac worked. But I don't, as a general rule, "see" them.
I'd like to study the concept a little more in depth. Can anyone post some games with pawn sacrifices in them? GM games; your own games; whatever.