I've always heard that you can prune
spring-flowering shrubs right after they bloom, but for fall-blooming ones, wait until late winter or early
spring.
I wonder if that's the same for
trees. I don't know. I always prune my
trees in late winter, so that bugs won't take advantage of the open cuts in the bark and move in. It's also easier in winter (for deciduous leafy
trees) because there are no leaves blocking your view of the limbs. I only prune a
tree in summer if it has broken limbs from weather or other accidental breakage. Then I trim off the branch where it comes out of the trunk, leaving a collar which is supposed to close over the hole, more or less.