My daughter has been experimenting with moving her body her whole life. At six months old she is not yet crawling, but she has now perfected a move I call the creeping roll.
This move allows her to move quite rapidly from one side of the room to another, and to retrieve any item she wants to explore. I very quickly learned it is no longer safe to keep my coffee cup on the floor!
I have always tried to allow her the space and time to learn and explore on her own. This means when I set her down, I put her only into positions she can achieve naturally and I allow her to figure out how to maneuver herself into different positions and over to toys without my assistance.
It has taken a lot of self-control on my part not to be rescue her constantly by handing toys to her when she struggles. However, the look of complete satisfaction when she figures out her own way to maneuver across the room and accomplishes her goal on her own, is well worth the effort it takes to sit on my hands!
Here is a short video clip of her practicing the creeping roll.
Here are two great articles on allowing babies to develop their motor skills naturally: