practice the boardslide motion on a piece of wood in your living room, basement, garage, backyard etc...
no matter what, concentrate on having your body perpendicular to the feature. That will help tons in not slamming front or back.
SA videos will help you a lot. Will give a great base knowledge to start safely. AND start on a small rail at first close to the ground. Hurts a lot less !!!!
-I'm Slyder and I suffer from "Gummer Syndrome"