your setup is imfortant too, many times beginners tend to slide onto the rail or come on a bit from the side so they do not have to turn as much to get onto it.  when coming into the rail, have a good centered stance and hands froward, just as though you were coming into a jump.  you should still pop like you would off a jump and this will allow you to land centered on the rail rather then in the backseat.  from there, just keep your weight forward, focus on the end of the rail and you should have it in no time.