If you write a business plan for investors, the executive summary is the only part that matters. Why? Because it's all they will read. Even if you don't write a full business plan, many startups will prepare an exec summ that they use in trying to book investor meetings. Needless to say, having a good executive summary is key to raising money.

My approach is not to write an actual document, but instead do a short presentation. Whether you do a document or a powerpoint, remember your goal is not to educate, it's to sell. Your sole mission for the exec summary is to get the investor to agree to a meeting. That's it.

Here's a good structure to follow.

Slide 1: company info (background, financing to date, financing sought), what we do (including business model), and value proposition
Slide 2: The pain or problem
Slide 3: The solution (what you're offering to the market)
Slide 4: Vision: Where are you going? How big can this be? How do you make money? Give a sense for just how much money you will make (but don't give full financials)
Slide 5: Key Sucess Factors - this is optional but it shows that management knows its stuff.
Slide 6: Team

That's it. 5 or 6 slides focused on enticing sufficient greed so that the investor will book a meeting with you. Try this structure in your business and tell me how it goes.