As a general rule of thumb, if the plant blooms in the spring, prune after the blooms die. If it blooms in the summer or fall prune early in the spring just as growth is beginning. Never prune between August and October as plants are preparing for winter. Prune as needed, not all plants need to be pruned every year. You can prune dead or diseased branches at any time.
When you are ready to prune always make the smallest cut possible. Prune for health and shape so you direct the healthy growth of the tree or shrub.