Give sweets to children. Wear a costume. Pretend to be scary. Girls dress slutty and when someone asks what they are ment to be the answer is usually "i'm ment to be your mum", which could be taken either way -- a good or bad thing (good cause they are saying your mum is good looking, bad cause they are saying she is a slut). I think halloween is overated.
Make pumpkin laterns. Apart from folk around here (North East England) have no idea what a pumpkin is, so settle for the poor man's alternative of a turnip.