Do a lot of sw bs 180 on flat, and then move on to sw bs 90 to tail on flat (imagen the obstacle or simply put a piece of tape on the table). This would help you to get the hang of the movements you need to pull it off. Then move on to sw bs backtail on a rail/ledge/curb and pop out untill it feels natural and effortless. Then its only a matter of getting the hang of throwing in a sw flip off the obstacle at the end. Dry runs on flat before going for the obstacle has always helped me advance a lot in a short amount of time..
