This is a good instructional video on how to do a round off properly.  The instructor discusses proper body alignment, landing hand positions, and practicing “snap downs” in order to make sure you don’t do a cartwheel landing instead of a round off.

I love how he breaks down everything into a step by step process and shows you what to practice.  If you have mastered the round off, how about letting us know in the comments below.  Tell us how long it took you from when you first started working on it until when you mastered it.