Always suppose that you only have one shot at your target. Whether it is an elevator pitch or a full blown presentation, know your audience and make what you say as relevant to them as possible. The best route to success is to be prepared; certain of what you are saying and to whom.
Investors speak for others' money, as well as their own, and they must be able to communicate your proposal to their investors with clarity and enthusiasm. Help them to help you by keeping it simple.
Know when you will be required to provide greater detail and be ready to share that in a manner which is understandable and uncomplicated.
You cannot over prepare for a pitch so practice, rehearse, revise and refine. Preparation time is not a luxury, it is essential.