The drawing on the left shows a young deciduous tree before pruning. Notice that the tree’s energy (growth) moves primarily upward, forming a more or less inverted triangle (tip down). In order to control this growth and move the energy down, prune to form the tree into a triangle (more or less) with tip pointing up.
The drawing on the right shows the same little tree a year or two later. Now your goal is to control growth and keep the tree’s basic shape by continuing to prune back vigorous upward growth (thus forcing energy down into the trunk and primary branches) and to eliminate unsightly and unhealthy growth (branches that grow in toward the center of the tree, branches that cross the trunk, branches that grow straight up rather than out, and so forth).