What is the most common mistake made when pitching your business to potential investors?

I have sat in a number of investor presentations, and in my view the biggest problem is not being able to present the pitch clearly and briefly so that the investor understands exactly what you do and why his investment will have extremely high odds of being a major winner!

Simon is correct - as far as some specific other issues that I've seen:
1. Product/technology looking for a market rather than designing a product/technology to solve a serious market need - this really means that they don't understand their customers and may not be talking to them as much as they should.
2. Don't understand or have experience in the market & distribution model that they've targeted for selling their product.
3. Too optimistic about the development time & costs for their product, the sales cycle, and the adoption rate by their customers. This unwarranted optimism results in financial forecasts that under estimate the amount of cash required to achieve either key milestones to allow the business to raise additional capital or to get to cash flow breakeven.
4. The entrepreneur(s) either do not have an "offer" ready to discuss with the investors or their offer is completely unrealistic and "puts the investors off". Remember that rarely will an investor make an offer to you and if you are unrealistic on valuation, you instantly lose credibility and likely the opportunity to work with those investors.
5. Too proud to admit what they don't know or to take advice or to be grateful and gracious even when the investor declines. No better way to "burn a bridge" with investors.

Good Luck!

Pitch Failure comes down to a few key things in the 10 minutes allotted:

1. Failure to pitch the problem, spending too much time pitching the solution.

2. Decision Making Ability: Investors listen with experienced ears and when they ask a startup what they will do with the money, the startup commonly will say the wrong thing. If the next best step is to hire a VP of Sales, but they want to spend the money on something else, they won't get funded.

3. Credibility: The accuracy of the business plan doesn't really matter. What does count is whether the startup has taken the time to consider fully the elements that belong in a business plan. Investors know that the projections are wrong, they are looking for an understanding of business and the product.

4. Commitment: Probably most important to the investor is the startup team. Who are they, their values, their commitment to each other and ulimately to the investor, they want to know who they are getting into bed with.

5. Valuation: Early stage pitches that overstate the valuation in the opinion of the investors will not get funded.

Pitching is an art and those who are most successful tend to get a coach.

I've been fortunate enough in my career to make investment pitches as a public company COO/CFO to sell side analysts and as a private company COO/CFO to VC & PE firms and the similarities are striking.

With both audiences, you need to be able to catch their attention in the first 5 minutes of your presentation. There need to be enough hooks to get the audience past the first 5 minutes and on to learn more about why they should invest. Otherwise, your audience will drift to thinking about the next meeting, etc. To that end, the first 5 minutes needs to crisply and concisely cover the following:

*The Company
*The Value Proposition
*The Market Size
*The Competitive Landscape
*The Disruptive Nature of what the Company does ( or technology developed)
*The Sources & Uses of the Investment
*The Financial Metrics of a Mature Business Model once Achieved
*The Exit

A lot to highlight in 5 minutes and if done effectively there will be enough hooks to get you past the first 5 minutes and on the way to a successful raise. Good luck!

Calling your presentation a pitch and controlling the time.
Most presentations are scheduled for an hour. In reality, one should plan for 50 minutes. I believe it is important to allow for 20 minutes of questions and answers. So, that leaves your presentation to be 30 minutes. That may appear too short but it is 10 more minutes than the typical time allotted if you are presenting at an investor conference.
Finally... practice, practice, practice and use trusted listeners.

Agreed.

IMO, the audience should understand within either/both the first couple of slides and the first few minutes who you are, the problem and how you solve it, and why you do it the best. And if using slides, it's best to present them rather than read them--it's agonizing to sit through someone reading every bullet point on a slide, especially if there is too much on the slide. And probably no more than 10-15 slides and 30-minutes of prepared presentation.

Just my thoughts!

The most common mistake in my mind is believing it is "one and done." Not all the time, but there is usually a relationship or warm introduction made that connects the entrepreneur and the investor. The entrepreneur should be focused on getting the next meeting and growing that relationship.

You should come away of every meeting learning something...how to improve the product, how to improve the presentation, how the investor looks at the offering. Use this learning to improve, in preparation for the next meeting.