Hey. I had a very difficult time learning crankflips. I started by riding forward fast, jumping and letting the cranks turn. This resulted in strange half crank flips that involved no actual kick of the pedals. I managed to improve them by pulling up on the seat as hard as I could, but they still were not good. I then gave up on them and learned other things. I eventually learned 90 flips, hickflips and treyflips. Then after that I tried two handed crankflips and they were easy. I could finally get the kick. My advice would be to use two hands, it will be much easier. You could also learn 90 flips first like I did, I found them easier to commit to. Here is a tutorial I made on hickflips, it might help:
http://m.youtube.com/#/watch?v=EFKbhVYZbZg. I hope that helps, good luck!
