I just recently learned them on the ground and this is the technique I used. The first thing you want to do to gain confidence is to backflip off the frame of your trampoline onto the mat. That way you have a pretty sturdy surface and a pretty forgiving landing, and its a level surface (starting surface and landing surface are the same height which would be a good simulation of the ground). Once you get those on lockdown and you are comfortable with throwing a backflip off a hard surface, take it to a rock ledge or something about 2 feet high with a soft grassy landing. This will help you gain more confidence with throwing it off a solid surface and landing on a solid surface. Keep doing this and work your height of the ledge lower and lower. Once you feel super confident off lets say a 6 inch ledge, go for it on the ground. Your confidence will be extremely high, and so will your success rate of getting it around and not getting hurt. Hope that helped!
Yeah.. I go about 2 feet back on mine. I think its easier to go backwards than to stay in the same spot. Well just a little backwards, not too much or else you have less time to pull the flip around. Just try going back a foot or two, you never know, might work out better for you anyway?