The Rock and Roll is very similar to the Rock to Fakie, another skateboarding trick. Before you learn how to rock and roll, you really should learn how to rock to fakie. You also want to have kickturns down, and feel comfortable doing them on a ramp.
Like with every other skateboarding trick tip, make sure you read though all of these instructions before you head out and try it. Make sure it makes sense to you, and that you can picture yourself on the ramp, doing it on your skateboard.