For this trick its is very important that your not scared of rails and nosepressing at fairly high speeds. 

       First, approach the rail with speed, the more speed the better (when your learning), because you do have to nosepress for a long time. As you come off the jump spot your landing, and try to land only with the nose of your board. Keep your weight far forward and hold it there. It gets difficult to hold it after a couple seconds, but with pratice you'll get better at it. Hold your position as you slide and then as you approach the end of the rail, you want to nollie off. This is done by, putting even more weight on your nose and then pop the nose up off the ground. Tuck up your feet so that the tail of the body doesn't hit the rail, now spot your landing, on the ground and try to land there. As you land absorb the impact with your knees and then ride away clean. Good Luck!

        When you get good with this trick, try do it much slower, it makes it look REALLY nice.