It's tricky. Usually you're going to call and then just play poker after the flop. Basically you have to consider your opponent's range and how well it interacts with the flop. If there's an Ace or two broadways out there, you can often just check-fold unimproved, but otherwise it's usually worth a peel. The trick is to think about other hands you could also have – don't fall into the trap of assuming your opponent knows you have a pocket pair. Remember that you might also check-call hands like draws or top pair, so your opponent can't just blindly barrel at you (and most won't). It's not going to be a hugely profitable proposition – there is no hugely profitably way to play middle pairs OOP – but it's better than the alternatives of folding reraising. You just have to do your best. Depending on the pair and the situation, it may be good enough to jam or 3b/5b vs a late position raiser.