Focus on an intentionally narrow market. It's like keeping a fire contained at first to get it really hot before adding more logs.
- Find out if there is a subset of the market in which you can get a critical mass of users quickly.
- Build something for yourself and your friends, who will be the early adopters.
- Among companies, the best early adopters are usually other startups. They are more open to new things because they haven't made all their choices yet.