For Briefmetrics[0], first 10 users were basically the people I was building the product for. About half of those immediately and enthusiastically converted to paying customers.
The next 100 were friends, people who follow me on Twitter/Facebook, and Show HN[1]/Show Lobsters[2]/Show Reddit[3]. Got a few more paid customers from this segment but the conversion rate was not great at all.
Now I'm working on the next 1,000 which will probably involve some "real press coverage" and some reviews on niche blogs or guest posts. This part has been the hardest for me and would love any advice/intros.
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[0] Briefmetrics [https://briefmetrics.com/], email summaries of your Google Analytics.
[1] Show HN [https://news.ycombinator.com/item?id=6641385], which annoyingly got flagged pretty early on and never got any traction. Considering doing another Show HN, but kind of worried about annoying the HN hivemind.
[2] Show Lobsters [https://lobste.rs/s/ppcmud/show_lobsters_i_built_briefmetric...], some good feedback, this went as well as I could have hoped for the size of the audience. Been really enjoying the Lobsters community.
[3] Show Reddit [http://www.reddit.com/r/analytics/comments/1uk9na/briefmetri...] Got a chunk of visitors, but all the comments were from people I knew so the feedback was a bit of an echochamber.