Avocado trees are evergreen trees that can grow up to heights of 80 feet depending on the cultivar. Avocados originated in Mexico, Guatemala and the West Indies, with the Mexican fruit trees being the most cold hardy and the trees from West Indies tolerating the most heat. There are many hybrids of the original trees. Avocados need pruning in the early years to shape the tree and later to keep it smaller. Fruit grows on the terminal ends of the twigs and if too much is pruned, there will be no fruit that year.
Prune dead, damaged or diseased branches anytime of the year. Trimming back the side branches of the tree can also be done anytime, since the tree is an evergreen. However, for each branch you trim you will lose the fruit, so only do a few each year.
Cut the tree back to do major shaping in January through April. Cutting side branches that stick out too far or cross other branches is necessary but can be done over a number of years. Cut the largest the first year, the next largest the next year and repeat until the tree is shaped the way you want it. Always cut these branches back to their origin.
Reduce the height of the tree in the same manner. Cut the tallest branch one year and the next tallest the next year. Over a period of a few years, the tree will be at a manageable height, and the fruit will grow thicker on the bottom branches. Cut the branches back to the original crotches.
Prune branches to open the inside of the tree to sunlight. Start at the top with a branch, then a little lower on a different side, and work your way around, cutting off three or four branches, depending on need.
Paint branches if this pruning leaves major branches exposed to very bright sunlight. Dilute some white latex paint, and paint it directly on the exposed branches. This will help reflect the sunlight and keep the branches protected from sunburn.