Limit the subject line to 50 chars.
Write like you’re giving orders.
Start with a verb.
One line often suffices.
Limit the body lines to 72 chars.
Explain how you tested the change.
You haven’t tested the change? Go do that first.
A template I like:
Add new feature
NOTES
-----
- This feature does X
- We did it because Y
- Also, it's related to Z
TESTS
-----
- I tested locally
- I went to the tool and clicked here and here
and then was able to see this and that