I targeted a niche (Japanese language learning) with communities that already exist and discuss resources intensively. Then I built what they're looking for (and what I could tell from other language communities that they would like but aren't actively asking for) and went to those existing communities where people already are to introduce it. I also actively respond on Twitter, Reddit, other niche forums etc. and plug my couple apps in non-intrusive ways when relevant. My users also recommend the apps within these communities. Some journalists and competitor publications also mentioned/reviewed my apps which helped, without me pitching them. I think the niche I chose to start with is particularly good because it is full of many tech-oriented people who already share and discuss resources, and has people who are fatigued with overly-configurable setups and are looking for easier solutions.

I have plans for pushing this much further (getting people to spread word of mouth more actively, virality elements, interesting ways to share content) but this was enough to get going and quit my job.

I also put keywords of some loosely competitive apps and former dead apps or Android-specific apps that people will still look for into iOS app store keywords so that my apps show up in search results. Technically not allowed but it is the norm and I see competitors do it with mine.

I also try to leverage everything I do in multiple ways, so that I have features I can reuse across other apps, a common foundation, etc. I'll start documenting these practices in the open under indiedevstack.com but haven't set that up yet.