Chris Beams: How to Write a Git Commit Message

Certainly nothing new (it's from 2014), but this is a very comprehensive article about writing great commit messages.

1. Separate subject from body with a blank line
2. Limit the subject line to 50 characters
3. Capitalize the subject line
4. Do not end the subject line with a period
5. Use the imperative mood in the subject line
6. Wrap the body at 72 characters
7. Use the body to explain what and why vs. how

Also, I like the way how Chris runs his blog from a public Github repository and apparently accepts pull requests on his posts (just click on the revision link on the post).