With the exception of your opponent holding AA (doubtful) or 66, you have the best possible hand on the flop. The board is safe for your set, therefore, you want to try to slowplay. Betting small gives your opponent more of an incentive to continue. If he has an ace, he will call. He may not give your puny bet any credit and raise you which is certainly what you want. Then you choose an action based on the turn card. In this case, the 8 of hearts creates a few potential draws to a straight/flush, therefore you want to protect your set and raise all-in.