I posted this on a similar thread a few days ago. For Standard Notes [0], here's what I did:

1. Comment on privacy related HN posts about a privacy-focused notes app. That would have gotten me 40-50 users.

2. Write articles [1] on encryption/privacy/webdev. Some of them made it to frontpage HN, some didn't. That might have gotten me to 500 users.

3. Repeat. Tirelessly. Painstakingly. Depressingly. Just keep going doing small things every day. Eventually they start to compound.

[0]: https://standardnotes.org

[1]: https://journal.standardnotes.org

Similar thread: https://news.ycombinator.com/item?id=14191161