Pruning apple trees
Pruning apple trees is the key requirement to getting good apples. A tree growing out of control will produce tiny apples and tiny leaves. When we first moved into our farmhouse, the seven apple trees next to the house were hardly producing fruit at all. One tree had thousands of little sucker sprouts, tiny leaves and no fruit at all. Another tree had too many huge apples. Although the leaves were nice and the fruit was large, most of the fruit could not be harvested because the tree was mostly too tall to reach with our tallest ladder. Pruning apple trees was not our area of expertise, but we realized that it was the most important thing to do if we wanted to rejouvenate the trees. The first year we pruned moderately and contemplated tearing out two of the worst trees. The next season one of the trees produced moderately, and the others did a little bit better than the year before. The following winter we pruned much more severely, and the trees all responded with bigger leaves, bigger fruits and healthier looking trees. After one more year of heavy pruning, we now have nice and very tasty apples on the trees that were previously the worst. In fact, one of our favorite apples was a tree that didn't have apples for the first two years we lived here.
When to prune apple trees
Apple trees can be pruned any time of the year, but a good time to do this is in the winter/early spring. The tree is in a dormant state, and without leaves, you can tell a lot more about structure. This is the time you can cut down some of the height of the tree. Which crossing branches need to be thinned out is much more obvious.
Summer pruning can be done to limit or direct growth and to cut out dead wood (you can't tell what is dead when the tree doesn't have leaves). And, as we do - feed the suckers to the goats.