small blister leave it be.
big blister with lots of pus inside, suggest poke it as Manager
said, but leave the skin there, it'll protect the raw area against
bacteria infection, which may be quite painful.
if the blister is in an area that encounter lots of friction, like
on the feet, then might want to put a plaster there. otherwise it's
better to leave it exposed to air. let it dry out.
