Three things...
1. Practice with scraps and no batting -- often it's the movement itself that is difficult to master, and you don't need batting to do that!
2. Practice with batting scraps that have been pieced together -- because eventually you'll do this on a real quilt anyway
3. Quit practicing and just go for it! If it doesn't look quite right, wash the quilt and then dry it on high. All sins will be forgiven, seriously.