Harvard Business Review has a very good four minute video on how Build a Flexible Business Plan,  Here are the take home messages:

1. Start from the heart: Only go after what you are passionate about
2. Think big but start small: Have a large vision but figure out small steps on how to get to it
3. Have a basic framework: PIMM – or People, Idea, Model (business model) and Market
4. Know your trade-offs: People are more important than Idea (A-team can improve the idea, but idea can not improve a B-team).  Idea is more important than business model (you can change a business model around an idea). And business model is more important than market (you can change the market applicable to a business model).
5. Keep it iterative.