I find it easier to spin of boxes... Maybe it is just me but I seem to get better footing for my pop. But when you spin off a box make sure to pop and thrown your head and bring thoese legs up... Also of course higher boxes are easier to spin more off of...
I actually have trouble spinning off boxes because my skis seem to slip when i go to push off. On rails I get on the corner of the rail and right before sliding off push and throw the hips around
well if your really on the rail locked on it will feel like your standing on the ground ... at 90 and just pop like youd normally pop on the ground and throw your hips with your eyes on your landing the whole time (270 frontide)
when you get close to the end of the rail kinda of turn the way you want to spin off then pop and finish the rotation. don't like jump of the rail though cause that looks gay, like you don't have any stezz...