The easiest way to do it is by leveraging the existent communities.
Search for places where your potential customers hang out and start to help people, ask for feedback.
I did it for all my last products, that's clearly the easiest way to start getting your first users.
It can happen sometimes yes, I've been roasted in a bad on some subs before.
That's really not the majority. What i understood afterwards was: the guys there weren't my target, my product didn't help them at all.
They felt like I'm promoting out of the blue, and i got my ass kicked.
That's true, I still get a few visitors per day from the post I made on /r/nocode.
If your post is in the top of the month/year/all time it will bring you visitors on the long term.
(I guess they're also better on Google search. Not sure tho)