How are you using Reddit for traction without being a spammer?

I'm hitting a wall trying to gain alpha users for a live app with a fairly specific use-case.

My fear of becoming "Spammy McSpamerson" has been so strong that I've paralyzed myself into doing nothing. I had been responding with useful advice here and there but I'm not sure when or how to bring up my solution.

I'd love tips from founders who've successfully used Reddit to naturally connect with people who genuinely need their product. How did you find the right communities, contribute meaningfully, and know when it was appropriate to share?