Sarah had good advice. If you really want to strengthen your legs to kick over easily, get into a bridge and do running kicks in that position trying to go higher and higher when each leg kicks. They are hard to do at first but will help develop leg strength. A Romanian coach taught me this one. It works!
i recenly got this move and it took me some time to get it what i did was work on doing it from lots of different hight mats untill i got to ground level and evey day i practiced bridge getting my shoulders over and past my hands also i got my mom to pull on my shoulders in bridge also work on your splits as they make it easyier
practice some more on the couch and with spot before trying it by yourself on the floor.
You may think you have it good, but the reality is you need to have lots of practice. Take if from someone who knows. I have been doing gymnastics my whole life and I am now doing double backs... it just takes practice.