[oleks637]

From my experience, you should first understand your audience, who they are and then find places where they hang out. Find groups on Reddit, LinkedIn and Facebook and post about your product.

Another thing you could try is services like Betalist. For my last project it worked pretty well: i spent 120 EUR on paid promotion and got around 250 signups. I can't say that they were all relevant to my product, but around 30% signed up for the app and used it at least ones.

[everling]

+1 for understanding your audience. My side project, an inspiration-based film recommendation engine, has a niche audience but is of little interest to the general public (or HN) or those that only watch Netflix+Disney/Marvel. My traffic comes from arts magazines, twitter and things like apartmenttherapy.com. So you have to seek out communities that may be particularly interested, then maybe the traffic will follow.

Then it's also just luck in getting noticed. I got a significant amount of traffic this fall from the Recomendo newsletter which led to someone reposting it on Reddit with a couple of thousand upvotes.

[oleks637]

I was lucky to get featured in a blog post by a french blogger, who was subscribed to the betalist and noticed my app. (What is also cool with niche audience, is that they are usually more eager to adopt your product in the early stage and give you feedback, which is great if you are only starting and need some solid feedback from couple people but not from hundreds)

[pc86]

Off topic but this is the first I've heard of ApartmentTherapy, that's a pretty neat site.