Answer:
You get a needle and hold it over a candle or fire and when it gets really hot pop the blister. The heat is to get the needle sterile. If the blister is in a high-use location, like inside the hand, you can prevent it from tearing open later by inserting the sterilized needle BESIDE the blister and coming up from the underside into the blister, then squeezing the blood or fluid out that way. The top layer of skin lays flat and can actually bond back together instead of splitting open. Good luck!