Here's an excellent article by Spencer Fry of of Carbonmade, about the importance of building out a very strong core capability before branching out into other domains.
Think Apple and Facebook — both launched with a single stripped down product — Apple's operating system (their hardware was just a delivery system) and Facebook's simple social networking: messaging and, more importantly, photo sharing. Both focused all their attention on building their trunk and then leveraged their core product to branch out.
Spencer also has some good advice for how to go about building this strong trunk: be patient, persistent, and focused.
Too many entrepreneurs think that they need to rush to become overnight successes or they'll never get there. They think it's a sprint and not a marathon. Carbonmade has been around for five years as of December, 2010. It took us three years to be able to work on it full-time, and then another year and a half before we were able to hire our first two employees. Carbonmade is only at 1% of what it'll be in five years. Patience, my friends.
Other than having patience, you need to build a stripped down, functional product that is focused on a special type of user, but at the same time something that can still be used by a more general audience. That way you aren't discouraging anyone from using it.
What's your company's trunk?
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