For the last product, which I shut down due to lack of traction, the most valuable leads I received was when my product got featured in a newsletter without being asked. I had posted a comment on a Blog post which described a complicated GA setup to achieve something that my product could do without effort and the author forwarded it to his subscribers.
I think that sums it up quite well: look for people who have the same problem as you're solving and pitch them your product. Any other marketing effort: paid ads, blogging, events require too much investment and I don't think they should be recommended if you're bootstrapping a small product.
I've used and seen this approach used to both validate, grow and shut down projects.
Build a list of people. Should be your target audience, but if you can't do that, find people that are adjacent or gatekeepers. Ideally this would be ~10 people, but if it's 3, start there anyway.
Go with a specific question/ask. Interview them. Then get them to ask you questions back. Answer as honestly as you can ("I don't know" is fine, but follow up with your suggested process).
At the end, ask who else you should speak with. If you're on the right track, your network and opportunities will grow. If you're not, it'll shrink to nothing. Repeat.
If there's a market for your product, there will be an alternative product for it. Like for me, I had a recipe app. My competitors were recipe blogs, Facebook pages, and groups. If you're building something SaaS, there might be a WordPress plugin doing the same thing.
Your product should be 10x better than the solution they hacked together. If no solution was hacked together, it's possible there's no market for it or that you haven't done enough research before building the product.
There might be some exceptions though, like a note taking app, where the competitor is a piece of paper with no community.
I wrote up a nice narrative a while back  on my two "first" products I built. The first "first" was on accident, and the second "first" was... kind of still on accident.