The amount of thinning that should be done depends on the type of fruit tree. These recommendations are general guidelines to allow proper fruit development.
Apples and pears: Fruit should be six to eight inches apart leaving only the largest, nicest fruit in each cluster.
Peaches: Fruit should be six to eight inches apart with only one fruit per cluster.
Plums and Prunes: Fruit should be four to five inches apart.
Apricots: Fruit should be two to four inches apart.
Cherries: No thinning required
Thinning can be done using pruners to clip off the fruit or by snapping them off by hand. Use caution to support the fruit as you snap to avoid breaking the branch. (Cynthia Domenghini)