I created a library that helped developers. It made a few hundred $ in revenue but nothing like I hoped.

Its an experience I've seen a lot. You think if you create a great product and advertise a little it will go viral - but in reality getting people to use it in the beginning is the hard part.

Next time I'll try to build the community before the product. Spend more time on marketing and less on coding.

Plus I think selling to developers sucks, esp now so much free and open source stuff around. Non-tech Users are probably better customers.