THINNING FRUIT
In years of abundant crops, primarily on Apple and Pear, thinning the fruit will provide many advantages:
Fruit Size - the resulting fruits will be much larger.
Return Bloom - next year the tree has a much better chance of producing a decent crop, as opposed to developing a habit of biennial bearing.
Tree Stress - with a lighter crop (fewer fruit) the tree is under less stress.
Flavour is improved with a lighter crop, most noticeable on highly flavoured types (e.g. Gala).
In June fruit trees undergo a process commonly referred to as June drop, when they shed some of the crop. If the tree is still loaded after this, perhaps mid June, consider thinning.
The apple flower produces a cluster of fruit. Using your pruners, remove all but one of the small fruits. You may leave the largest, and/or remove damaged fruits. For apple and pear, thin the fruit along the branch to 8" apart.