The best discipline plan is excellent teaching, however in the real world incentive plans are sometimes nice. During the quarter that we study the Solar System, I use a collection of pictures of the planets . I print these onto label paper to make stickers. I also make a stamp collecting book where students put the stamps as they earn them. Under each stamp is a box with information about the planet stamp that is needed there.
Students earn the stamps for correct answers and other good deeds.
When students have collected all 12 stamps, they turn it into me for a pack of Starburst candy. Students love to earn the stamps and the fact that they have to stick each one in the correct place helps to reinforce the concepts of our science unit. You could design stamp plans for many units. I have another one with pictures of Virginians who were important during the Civil War. I usually cut up the stamps and place them in a bowl on my desk.