You should fold pre-flop whenever your hand is unlikely to be profitable based on your position, stack size, and the action before you. Weak hands like low offsuit cards and dominated combinations are usually easy folds, especially from early position. If there has already been a raise or re-raise, it's often better to fold marginal hands rather than play difficult situations out of position. Good pre-flop discipline saves chips, avoids unnecessary risks, and is one of the biggest differences between winning and losing players.