I did maintain an opensource project for a while and that taught me how to do it correctly:

• Don't. Just don't.
• If you really, really want to, just do what you need to fulfill your needs, never do something for someone else.
• If someone is really insistent, say you'll do it if that person pays for the implementation of the feature, and use your day job's hourly rate for it.
• Then don't implement anything you don't want to, because nobody is going to pay for it anyway.

Or to put it differently: Never see your project or contribution as anything more than a hobby. You will never see an return on investment.