As a maintainer of dozens of fairly small OSS projects on GitHub, I learned early the importance of 'No'. Also, unmentioned here, you have to be willing to ignore the 'me too' present in a lot of PRs and feature requests; what's most important to me is 'will this new code/feature make the project easier or harder to maintain?'

If harder, it had better be a stunning new addition that makes the extra maintenance worth it... And often, it had better include an automated test!