When you edit other people, go to their desk and sit down with them. Start by telling them what they did right. After the praise, go through your edits one by one. Cite the principle behind why you made the change.
If you only send the redline, the person you're editing will click "accept" on all of them and learn nothing. You'll make the same edits next time.
Every time you edit is an opportunity to teach. When someone learns to write better, that's time you get back.