Summarize the following:
Once your tree is bearing fruit, you will notice that its main lateral branches get weighed down by fruit. These are branches you'll want to keep at the next pruning time. You will see other branches that are growing vertically, or some that look old or weak. Make notes of these vertical, old or weak branches that you should prune the following year. Your tree may take a year off from fruiting every other year. Light annual pruning is still a best practice for encouraging new growth. Branches growing straight up, especially those near the top that are thin and weak, should be removed. You also want the inside of your martini-glass shape to not be dense with vertical branches, so remove those as well. A rule of thumb is that a bird should be able to fly through your olive tree. If your tree is too dense with vertical branches in the middle, a bird would not be able to do that, and you should remove more vertical branches. Fruit only grows on lateral branches, so another reason to prune these vertical branches is to give your tree more energy to put toward fruit-bearing branches. As your tree ages, some of the lateral branches growing off your main branches may become old. When you observed your tree at picking time, these are the old branches that maybe bore fruit at one time, but they have stopped. Cut these branches to encourage your tree to grow more fruitful branches. Any growth below the main fork of the tree, going down the trunk to its base, should be removed. These branches are usually small, grow vertically or downward, or otherwise look out of place to your tree's main shape. You can remove these suckers any time of the year, whether its your annual pruning time or not.
Observe your tree at picking time. Remove vertical branches. Cut lateral branches that have become exhausted and weak. Remove suckers from the trunk's base any time.