Ask HN: How do you develop a userbase for your side projects?

For a while now, whenever I build something on the side, my single biggest point of difficulty is getting users and increasing user count month to month. Certain projects I get enough users to initially validate the idea as good or bad, but after that point it's hard to continue to build and grow a decent userbase. I know there are many talented individuals here, so I guess my question to you is what tips and tricks do you use to build and develop a userbase?