Xtremehorticulture of the Desert: Thin Your Peach Tree While Fruit is Still Small

Thinning fruit, or selectively removing fruit so remaining fruit gets larger, should be done at an early stage of fruit development. See examples of the spacing of fruit for good size.
Flower removal so there are fewer fruit to pollinate can be dangerous if the tree does not get a good fruit set. Wait for fruit which was not successfully pollinated to fall from the tree. This should be just a couple of weeks after you see the fruit starting to develop. A gentle shake of the limb will confirm if the fruit has set or not.