The MIT Unicycle Club uses this method to teach people how to ride.
1.)Get two friends to stand on either side of you and get up on the unicycle with your arms around their shoulders.
2.)Sit up straight; look straight ahead; weight on seat, not on pedals. Rock the pedals to get a sense of balance. Get the pedals level; this is when you are in control.
3.)Pedal half turns then stop. Then full turns, two turns, etc. Doing multiples of half turns (from pedals level to pedals level again) is harder than continuously pedaling, but keeps you in control.
4.)Switch to holding on to your friends' wrists.
5.)Switch to holding on to one friend's wrist.
6.)Go off and use a wall instead of your one friend. (If you can't find a wall and a flat surface to ride on then continue with one friend, but let go as much as you can.)