For front walkovers--
I taught my friend how to do one, so maybe i can help!
First, try it on a trampoline if you can. Most people have the problem of not being able to "stick" it or basically they land on their butt. So if you're problem is..
Falling on Butt?
You're probably almost there, but you need more speed/power and when your first foot hits the ground really block off your finger tips and pull your chest forward.
If you land in a bridge?
You're definitely not pushing forward enough and do NOT let your second foot meet your first. They should be split the whole time. Read the one above!
I spot my friend on the trampoline by putting one hand on her back and forcing one of legs over. I always told her when she was coming up from the walkover to "spot" something and pull yourself to it.
I need some tips myself, though. My left hand comes off the ground late and i kind of twist a bit. Any tips for that?