Ideally the tree or shrub selected should be allowed to mature without any management to control it's size.
There are however many circumstances when pruning is necessitated, to direct growth where it is required, to restrict growth where it is not, to stimulate flowering/fruit or to remove defects i.e. crossing branches.
When pruning, leave a small collar, do not take right back to the trunk/branch, the smaller surface area, will make it easier to heal.
Pruning should be planned and reviewed as you progress, we often advise to do it with a drink in the other hand, it will slow you down. Visualise the flowing of energy and pruning diverts the energy where you need it or away from where you don't.