My first step after getting that one user was to "do things that don't scale". So I sent him/her a personal email letting them know I hoped they found the service helpful, and that I'd be happy to help out in any way possible. And to tell a friend.

No response yet!

For the current stage, this is the most important piece of advice. Everyone else is right: promotion is important. Sharing the product here, on Facebook, Reddit, etc. are all fine ideas, and asking your co-workers to try it out will be a great step as well.

But you want to present the best possible version of the product to your co-workers, friends, and family. So ask your one user a couple questions, along the lines of:

* What do they like about using your product? What problem does the product solve for them?

* What do they dislike about using your product? (What problems does it create, or leave unsolved?)

Beyond that, make sure that the UI is good. Then start promoting by the ways that other people have suggested.