1. Rewrite until you eliminate repetition, unless its intentional and for a specific purpose.
2. Dialogue should have a clear purpose. Whatever that it is, stay focused on that purpose.
3. In many cases, less is more.
4. Avoid prolonged exposition.
5. Pay attention to how natural it sounds: do they really talk that way?
6. Characters should have their own speaking styles!
7. Don't be afraid to have one character interrupt another! It happens in real life, too.
8. Pauses can be as important as the words themselves.
9. You can begin a dialogue scene in the middle of a conversation.
10. Read aloud to check the convos rhythm!
Follow these tips in moderation and your dialogue writing should improve!! :D