How to Write a Git Commit Message

The seven rules of a great git commit message

Keep in mind: This has all been said before.

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

From http://chris.beams.io/