it all depends on the type of faucet you have. the principle in nearly the same with them all. you need to remove the top off the tap itself and then you should find a screw. remove the screw and take all the bits out.inside you should see a washer(usually black circle). take it down to a hardware store and get them to sell you an new washer. take home and put back together. that should cure your problem.
Crash, August 2006