Generally speaking, typically it's best to prune your trees during the winter seasons - they're easier to prune because:
1) During this season, trees can heal themselves more easily
2) Naturally, there are fewer leaves because they've fallen off! This makes it much easier to trim.
3) Often, trees aren't as vulnerable to diseases and insects during this season.
This being said, different types of trees have different "best-to-prune" seasons. It's best to ask a tree service professional that has that knowledge.
Call us today for some advice.