Pruning olive trees is necessary to reduce the effects of alternate bearing tendencies of the Olive tree.Remember new growth will bear the olives,so the goal is to have a respectable crop with new growth.
Pruning cuts are potential entry points for disease carried by water so always prune after the rainy season best during late spring or summer.
There are two basic types of cuts,Thinning cuts and heading cuts.Thinning cuts are cutting something out and heading cuts are cutting something off.Heading cuts stimulate more growth because cutting off the tips of the shoot remove hormones that suppress growth from lateral branches.Most growth will occur close to the cut.We are trying to prune to let light in shaded areas will produce less olive fruit.
During a heavy crop year I like to prune just after the fruit has set so I can do selective pruning to thin the crop and stimulate vegetation.
Another way to manage for alternate bearing is to water and feed trees on heavy growth years to stimulate vegetation growth.