As several others have mentioned here, I was not focused on "launching the product". I was persistent about creating a solid and valuable product, and making it available for the entire world. I researched everything I could about building websites, particularly performance and SEO. The project was a learning project for me - it was technically "launched" since the moment I bought the domain. I continually iterated after learning new things about the web, and after coming up with new ideas. The growth came from a steadily increasing SEO presence and Social Network presence. I never once saw a code or feature iteration cause an immediate flood of attention, even when I gave them a little nudge on social networks. I will admit though, that I never attempted an all out launch of anything.
The project is mainly a fun site, but it has become one of the best tools for creating animated GIFs and memes on the internet. There have been a few big spikes from various press events, or Reddit frontpagers, but the true value has come from continually making the product better and slowly gaining the trust of the internet.
I'm certainly much newer to this than many people here, but my first big project now makes enough profit to support me fulltime, if I were to choose that (I work at another company as well). The site is imgflip.com if you're wondering.