Try doing it on a hill, when you flip you spin easiar. I used to do it in primary school but not i can't be bothered trying it, i never got to the stage of acctually doing a backflip on flat ground. I have a friend named Glen he can do back flips any way, he can run up a tree/wall and back flip off, he can rune and do sucide back flips ( Run forward and do back flip ), he back flips on his trampoline, everywhere, even flat ground. He show's it off so much lol.