You’ve all heard of the infamous elevator pitch—the three to four sentences that describe the essence of what your company does. It’s the first opportunity to hook in your investor. It’s the entry point that will (hopefully) result in a deeper discussion about your company.

A well-crafted elevator pitch will make people want to know more about who you are and what your company does. A poorly crafted one, on the other hand, could close the door to a potential investor. Because you typically have no more than 15 to 20 seconds to leave a lasting impression, you need to make those seconds count.

Here are the top ten rules of the elevator pitch:

1. Keep it simple.

Simple is always better than complex. While it is certainly true that some great innovations are extremely complex, the value or benefit of a great innovation is obvious – at least after the fact. You need to bring the obviousness of that value to the front.

2. Be engaging.

What’s the difference between being interesting and being engaging? Interesting is an intellectual response; engaging is an emotional response. Emotional responses are always more compelling.

3. Avoid negatives.

Create positive energy. Don’t disparage the shortcomings of your competition. Show how you can create a better future. You want your audience to feel enchanted, not battered.

4. It’s not about you.

Make sure your value proposition is customer focused, not technology centric. Your solution may be five times faster, and you may be a genius, but how does that translate into customer value?

5. Anticipate the obvious objections.

The most common investor reaction to a short pitch is, “Haven’t I heard this before?” You may need to simply explain how this is different, or why the time and the opportunity are different. You might preempt by posing and answering the question yourself: “Why have all previous attempts to build a fusion reactor failed? Because they didn’t [whatever you are doing]…”

6. Avoid purple farts.

Don’t use adjectives or phrases that sound pretty but are really just so much gas. Our favorites: Proprietary, disruptive, next-generation, synergistic, 2.0, world-class, 3.0, and “60 years of combined experience.” Avoid sweeping generalizations. And never say “nobody can” or “we conservatively project.” Even if what you say is true, you will lose credibility.

7. Don’t go overboard with numbers.

Use one or two numbers, if you can, to provide the magnitude of your benefit, but don’t jam bunches of numbers in. And don’t make your listener do the math (“We project our market share will be 18% of the $235 million market in three years”).

8. Maybe it is about you.

Your pitch may be something about your team that convinces us that you are the only company on the planet that can pull off what you intend: “My co-founders and I built PayPal from $0 to $100 million.”

9. Is the problem clear?

You might be able to best frame your statement in terms of the problem you are solving, rather than the technology you have invented. Frequently, the problem is obvious and doesn’t have to be clarified, but often the entrepreneur thinks the problem is obvious, when in fact it isn’t to the listener. You might need to say: “Vibration can reduce the performance of hard drives by 75%.”

10. Don’t lie.

You would think this goes without saying, but in their enthusiasm for their creations, entrepreneurs tend to slip across the line all too often. Please do not interpret the need to sell as a license to hype, exaggerate, misrepresent, spin, or lie. The best salespeople are credible and trustworthy. If you lose the trust of your investors, customers, or employees, then you are lost.

Once you craft your elevator pitch, try it out, and continuously improve it. The great thing about the elevator pitch is that it should be effective with almost anyone you know. Start with your spouse and your business colleagues from other businesses. In particular, you should seek out people you know who have good BS detectors and will be honest with you. Then once you have nailed it, make sure everyone in your organization has fully internalized it and can repeat it in emails, at trade shows, on voicemails, in press releases, at cocktail parties – and in elevators.