Be objective. Stick to the facts. Investors will have heard it all before, so get rid of any hype or ludicrous claims for your 'revolutionary' product.
Make it attractive. Use charts to keep it light on the eye, but put big chunks of data in appendices. Don't jazz it up with wacky fonts - keep it simple and authoritative.
Be methodical. Your ideas and language should be clear and concise. An investor won't sit through waffle. Curb your urge to push too many envelopes or think outside too many boxes. Business jargon makes you sound unimaginative, not savvy.
Get help. Chances are your target reader won't be an expert in your field, so give your plan to someone who is, then mine them for informed opinion and mind-blowing statistics.
Keep it up-to-date. A plan isn't a closed book - modify it as your business grows to keep it dynamic and to measure progress.
Write your executive summary last. This is the make-or-break part, so put time into it. Confine it to two pages and treat it as a showcase for your business. There'll be no stopping you now.