Simply work away at creating good content that can be found "naturally" by Google, try your best to get your site out in the view of other "niche related users" (yes, this can be by "posting" links on reddit ,or other sites that allow it, to relevant content.
There is no "silver bullet" now to get traffic... it's not like 10 years ago when you could simply spin a site up and generally get decent to excellent traffic.
A prime example is my site... don't have a lot of "users", but have some decent articles and even topics that are ranking well in Google searches, and since they are a fairly "standard" search term, I'm getting hits, if not necessarily registered users.. but I'm kind of an oxymoron.. I'm not so much into getting as many users as I can, but more into "distributing knowledge" to others. Does that have something to do with my age and my personal philosophy... you can pretty much bet on it. Unlike some, i'm not in pursuit of those "endless users" but more to the "distribution of information". Funnily, that latter can easily lead to the former. Ironically, way to admins don't realize that... they being in the ultimate pursuit of "registered users", many of which NEVER provide any content, meanwhile they languish in providing pertinent content that can't be easily found elsewhere for their site. Guess they still live in the era of the "Field of Dreams". I'd rather have 10-15 users that are very active than 500-1000 that are rarely active.