In accordance to the ANSI Standards, followed by ISA Certified Arborists, there are proper ways to trim and prune trees. 

Standards of Pruning:

• Risk Management

• Health Management

• Structural Development

• Providing Clearance

• Size or Shape Management

• Visual Appeal

• Production Management

• Wildlife Habitat Management

No-No's of Pruning:

• Topping 

• Lions-Tailing