Lean as far forward as you can (balls on the stem) while pedaling and when your strongest leg is at the bottom of your stroke, lock that leg. It will push you up and forward, when this happens pull up with your other foot. It's too easy to skid on grass and a technique that works on grass won't transfer to dry pavement (at least it didn't work for me). When I started riding fixed, the first time it rained I skidded up a storm and when the streets dried I had it down. If you have to, take a hose to the street and go to town. Oh yeah, and the faster you're going the easier (but scarier) it is.