Forgot to mention but it really helps to have a gear ratio and learning how to skid ambidextrously (being able to skid with either leg forward) to maximize skid patches.

AND... that you don't have to skid everytime you want to slow down or stop. Try hop skidding (if you're unsure what this is watch a FSFG video, it's what riders do before attempting a trick) and back pedaling to moderate speeds.