If pruning is needed, we usually do it in January. In areas with milder summers than we have, it is often recommended to prune them just before midsummer, because the cuts heal faster then, and the effect on the canopy is more visible.

In most species, regular heavy pruning isn't needed or recommended, but occasional selective pruning may be needed for shape and structure. The only regular pruning needed is to remove any dead wood. If you cut a branch, always cut it back to its origin, or to a side branch at least 1/3 as thick. If branches cross, cut out one of the pair, usually the more vertical of the two. Cut off branches that make too narrow a crotch with the trunk or other branches--they tend to split in high winds and heavy snow. If it is a Japanese Maple, let your inner bonsai artist run free, but don't worry about all the twig cutting recommended for tree and leaf size control. I would start inspecting the tree now, and have a plan in place before cutting!