If you want to build something, and aren’t certain what yet, start by making work that brings people together.

In other words, build a lighthouse for people to swim towards and congregate. Add value to their life—through insight, delight, or convenience.

Analyses, templates, and free job boards are all great examples of lighthouses. (Memes can be too.) The more insightful, useful, or entertaining they are, the more people will tell other people about it.
Elaborating on the work of Matthew Kobach.