I really like this short list of how to be an ally, although I would add an 11th: you will fuck up, so surround yourself with people who both expect and can accept apologies when you do. And obviously, be willing to admit when you have.
1. Don’t derail a discussion.
2. Do read links/books referenced in discussions.
3. Don’t expect your feelings to be a priority in a discussion about X issue.
4. Do shut up and listen.
5. Don’t play Oppression Olympics.
6. Do check your privilege. It’s hard and often unpleasant, but it’s really necessary.
7. Don’t expect a pass into safe spaces because you call yourself an ally.
8. Do be willing to stand up to bigots.
9. Don’t treat people like accessories or game tokens.
10. Do keep trying.
Do check out the whole list for the clarifications and explanations.