Contingeny contract

Think of something that you were going to do for or buy for your child anyway. Then gather paper, pencil and your child. Brainstorm together about the contingency, if______, then__________. 
For instance, you might say that they get one sticker, or one marble in the jar, for each complete practice session. Once there are a certain number of stickers or marbles, your child gets the prize. One of our parents set up a program where it takes a certain number of points to get a $3 prize, another number for $5 prize, and still another for a $7 prize.  She keeps the plan going for as long as it works.
Remember, all of these practice tips are valid, but usually what works for a week or two or three, won't work for six or eight in a row! The trick is to do the change up before they lose interest with the tip/strategy you're currently using.