Sequoia Capital has a good post on a simple, but comprehensive list of things they look for in a business plan. Meanwhile, as a handy toolkit, I regularly revisit a simple four-dimension checklist of a startup.
2PM – People, Product, Market, Money.
The priority among the dimensions shifts depending the stage of your business. Think of it as a juggling, instead of a one-way flow. You don’t want to dwell on a single dimension for too long, and other balls might fall out of your hands.