Tips before open-sourcing a project?

I'm getting ready to open source a 2+ year project (a calendar app). I'm trying to make things attractive for potential contributors, so I'm:

• creating a docs site and cleaning up the code.
• letting devs in the niche know via direct outreach
• considering doing a quick & minimal launch on Product Hunt

Anything else I could be doing to increase the odds of devs finding and using the code? What else should I be considering beforehand?