First get good at frontside 50-50s and backside boardslides. Ride up to the rail like a bs boardslide but with the angle of a fs 50-50. Ollie up and turn your body so that your trucks land on the rail. It is a little bit harder to balance these as compared to a fs 50-50. Comming off is just as easy as a fs 50-50. Practice these for a few days. Remember to do them fully backside. Don't be a wimp and hit them straight on and tell your friends you did a bs 50-50 because that would be gay.