"Back in the day" I remember it was as easy as sharing with a few friends or posting on HN, and it would quickly get some traction. Now it feels as if you need marketing clout.
The reasons you might care are -- to get more contributors, to make the software more sustainable; fame for your yourself or your company (how valuable is this?); etc.
Being clear on what benefit (if any) you will get from the project being more popular will make it easier to guess whether the 'investment' will be worth the 'benefit'.
But how do you do it? I think you've got to not just 'advertise' in general interest places like HN. You've got to find the community of people who will find your code most useful (perhaps people in the same business domain as you are working), and advertise to them, sometimes direct one on one. Conferences and meet-ups are good for this.
I think you've also got to have really good docs, and really good release management practices (semver, no backwards compat bugs, no encouraging using off 'master' instead of a release, good release notes, etc).
And if still nobody is using it, then I guess they don't actually find your software useful!
Get engaged with the community. Follow folks building stuff in your ecosystem on Twitter. Follow them on Github. Then mention them when you release something cool, make good screenshots and a nice intro. It takes one tweet about your project to go heavily retweeted before all sorts of people interested in your future work follow you, and so it goes on and on.
Of course this will only happen if your project is explained well, integrates into your ecosystem's package management, etc. Make sure it looks as tidy and maintained as other popular open source projects you know and love.
Finally, don't forget to star your own repos. This puts them into GH newsletter the next day (“starred by people you follow” section, assuming you already got someone following you), and also will put these repos on your profile page above your forks of other people's projects.
I was not aware of this. Thanks for the tip!
2. Have a ton of examples in the repository
3. Use it in production in your own stuff
4. Keep a solid change log and upgrade guide
5. Ignore the stars, all of this is for your team.