Fruit trees require thinning and shaping for them to continue to produce fruit. Left to their own devices, they become overgrown and the fruit will be small and misshapen.
It doesn't require a degree in horticulture to become good at pruning; practice makes perfect. Learning by doing is the best way to gain confidence. A few rules about what to do and when will be all you need.
Fruit trees are dependent on us to shape and thin the branches. Without our intervention, they'll grow lots of competing branches and eventually they'll be lucky to produce a few wizened apples.
The rules for pruning are simple; remove dead, dying, crossing or diseased branches.
I like the one about making sure there is enough room for a robin to fly between the branches. This gives each branch enough space around it to provide sunlight on all the leaves.
It's important to shape the tree in it's first few years, even if that eliminates the fruit spurs, which is where the flowers and the fruit form. Start 'em young, I always say. Then you avoid having to cut off major branches to get it back under control.
A scaffold of branches that will be at an angle to the trunk (making a good strong join) and even distance between each branch so that sunlight can reach into each leaf is the aim. There are several ways to form the scaffold;
A chalice or goblet shape is commonly used so that the tree doesn't get too tall. Picking fruit from the ground is much safer than from a ladder or scaffolding.
Each branch emerges from around the same height on the trunk, and then pruned to form an upward curve.
In time, these branches will form other smaller branches, and once the fruit forms, they will end up almost horizontal under the weight of it.
Another scaffold shape is in tiers, with several layers of branches. These are best in an orchard situation where it's more convenient to pick the fruit with mechanical implements.
In the home orchard, I like to have a low growing tree - most grafted trees will be grafted onto a dwarfing rootstock, which makes it possible to keep them small and compact. There's nothing like standing on the ground and picking fruit.
Apple trees, along with their cousins, pear and quince trees should be pruned in early spring, before the sap starts to run which is a fancy way of saying before the leaves start to bud.
In some methods of fruit tree pruning such as espalier (training a tree to grow against a wall or trellis) there is also some summer pruning, but for ordinary pruning, stick with the one time in spring.
Prune, plum, apricot and peach trees should be pruned in August so they don't bleed, or leak sap. The reason? The wounds won't heal and the sweet sap can attract ants and other pests, as well as mold.