The easiest way to find an idea is to target a big company, research it, figure out what are its potential next moves, then do it before they do it.

The fundamental advantage of a startup is that you can move faster than most big companies, and you need to use that to your advantage where it matters.

Here is a tip: if you can, try ideas that stay away from "advertising" as the main source of revenue, companies like that rarely become profitable quickly.