There are several factors that go into pruning; how and when.
The type of plant or tree is most important along with your growing zone.
Many trees and perennials do require or is best to time pruning while they are dormant or just prior to leaf break. This is not always the case, such as Birch Trees. Birch Trees should be pruned in Summer.
Many blooming plants should be pruned following first bloom, so pruning in Winter or Early Spring will result in removing the seasons flowers.
If you can give us more specifics we would be happy to help you with your garden.