Fall is a good time to prune
Fall is a good time to prune most trees and shrubs. However, there are a few that should wait until spring. Spring flowering shrubs like lilac, spiraea and forsythia already have their flower buds formed for next spring. Pruning now will remove many of those flowers. You might as well wait and enjoy the flowers and then prune them shortly after bloom.
The best way to reduce the size of shrubs is to prune one branch at a time. Select the longest branch and prune it back an inch or two shorter than the size you want the shrub to be. If possible, prune just above a side branch. Pruning a little shorter than surrounding branches will hide the stub. Then take the next longest branch and shorten it the same way. Shorten branches on the outer edges more than the top center to maintain a rounded shape. Lower side branches should be shortened less than upper ones so they are not shaded by upper branches. This is better than shearing all the branches the same length. It maintains a more natural shape without an outer shell of stubs.
Most deciduous shrubs can be shortened as much as one third. Beyond this point it may be better to replace a plant with a smaller growing one. Needle evergreen shrubs should not be reduced so much that there is no green growth remaining. They will not produce new green growth on brown branches.
Shade tree health and appearance can be improved by removing broken branches or branches which cross or rub against each other. Remove branches which grow up or in toward the center of the tree. Leave branches which grow outward. It is usually best to remove the entire branch rather than shortening it.
Upright conifers like spruce and pine sometimes have their leader branch damaged and develop multiple leaders. Save the most upright growing leader and shorten or remove other competing leaders.