Nice schefflera! If your goal is the keep it short and compact, then Shibui is correct. If your goal is to reduce the size of the leaves, then defoliate. You can defoliate every year if the tree is very healthy as yours seems to be.
I usually defoliate and prune at the same time. Defoliation helps me to see the structure of the tree and make good pruning decisions. I almost always cut the growing tip of each branch as part of this process. This encourages back budding and ramification--difficult to achieve with this species.