I taught Reece to crawl by getting him in a down then luring him under chairs with bars low to the ground. I'd put a treat trail and he'd crawl along the floor under the chairs.

After a few times of that, all I had to do was put a treat in front of him while he's laying down and say "crawl".

I know how to teach rolll over without physically rolling the dog yourself, but its sort of hard to explain without showing you. Hmm.