start off with easy ones. Most rivers are chock full of little holes that most people float right by that are fun to get in and sidesurf and just explore. Not only will you get lots of roll practice in conditions similar to what you will normally need to roll in on the river, but you will learn to understand holes which will come in handy.

Even if you don't consider yourself a playboater, get in holes for the lessons it teaches you about water.