The most important prerequisite for the moonkick. Try to land comfortably on one foot with not much of an impact, before you move on to learning the moonkick. That will make sure your gainer has enough height and that you have a bit of awareness, while you’re in the air. Don’t worry if your gainer is not fully inverted. We’ll perform the moonkick off axis anyway. You can work on inversion levels as you progress.
Note: You can absolutely learn the moonkick before you learn a normal gainer or slant gainer. However it may be harder to invert and flip, since you're not used to it yet.