My son has mastered the roll over and been working on scooting for about 3 weeks now. He spends a lot of time in his rain forest jumperoo, because he loves it. He jumps like crazy in it. I think because of that his legs are really strong.
To help him work towards crawling I have been giving him tons more tummy time. I have been putting favorite toys just out of reach and I don't have a crawler yet. I have an inch worm. My son is officially a scooter.
He pulls his legs up close to his body and then uses them to push his body forward. By doing this he slowly inches his way to whatever he is after. Except when he gets tired then his face gets pushed down and driven right into the carpet. That doesn't stop him though he just keeps pushing on with his legs. Honestly, I am surprised he doesn't have rug burn on his forehead.
Still it is the cutest and funniest thing I have ever seen.