For the health of the tree
Firstly, remove all dead, dying and diseased branches. It is a good idea to wash your tools after this stage and between trees with bleach, alcohol wipes or bottled methylated spirits (10%) then rinse, so you don’t spread the disease through the orchard. Next look for any branches that are crossing, rubbing, or growing in a direction when loaded with fruit will get in the way of another branch.
To ensure the plant can hold the fruit
Then look for branches with tight V (crotch) coming from the main trunk. The tighter the angle, the more likely this branch will snap when full of heavy ripe fruit. It is best to nip these out while they are young. It is quite upsetting to find a large branch of almost ripe fruit hanging precariously from your favourite tree. Branches that grow downward as these can also be dragged down when full of fruit and risk breaking and damaging the tree, so cut these off.