Pruning apples and pears can seem so daunting that some gardeners just turn a blind eye to their fruit trees. But pruning is, in most types, essential to maintain vigour and healthiness. The younger they are when you start, the easier it is to keep them in shape.
In bush-type trees (as opposed to fancy cordons or espaliers) aim for an open "chalice-shaped" growth that allows air and sunlight to reach the branches. In a young, newly-planted tree, choose 3 or 4 sturdy laterals (side shoots growing from the main stem) to form the framework of this chalice.
Take the leader (the central stem that grows tallest and points straight up) and run your hand down it until it joins one of your chosen laterals between two or three feet from the ground. Prune away the leader at this point. Remove all laterals except your formative three or four. Cut these back by about half or two-thirds of their length. They will fork in the next season and eventually form your eight or 10 main branches.