You need to be very good at bs boardslides, fs 180s, and fs 50-50s. Ride up to the rail like a fs 50-50. Ollie up and when your trucks are over the rail turn your back truck over the rail to land on it like a boardslide. You balance this out kinda like a boardslide but it will be a little different because you are leaning over to the side. Comming out is a little bit harder than a boardslide. You have to put more force to turn out regular but it is easier to come out fakie. Practice these on a rail about 8 inches high then work your way up to the big ones. Don't be like me and lean forward cause you will stick and fly to the end of the rail and slide on your balls. That shit hurts.