To kick start his ridesharing idea that ultimately became Uber, Travis Kalanick picked up the phone and started to cold call limousine companies. Today, Uber is valued at $51 billion.

Like any type of marketing, cold-calling done badly will waste time and damage your reputation. Here are seven tips to start you off toward your first $51 billion in sales.

1. Buy a List

Buying a list allows you to target the right type of client or customer. The list you buy should mirror some of your best clients. Proper targeting means you can clone your best client. Who doesn’t want that?

When calling consumers, never, ever use the White Pages or an online directory as a call list. Otherwise, you may find yourself on the wrong side of the Do Not Call regulations.

2. Respect Do Not Call Requests

When calling residents, it’s imperative that you register with the National Do Not Call Registry to scrub your records. You’ll face stiff penalties if you call people on the DNC list and they file a complaint.

3. Use a Script

Prepare in advance what you’re going to say. Just be sure not to sound scripted. That means practicing and tweaking your script until it sounds conversational.

4. Be Interesting

What’s most interesting to the other person is their own self-interest. How can you make their life easier, alleviate their pain, save them money, or make them sexier, healthier or wealthier? Talking about what you do or how you do it is the fastest route to the all-too-common “I’m not interested” response.

5. Get to the Point

You have a brief window of 30 to 40 seconds in a cold call to be interesting enough to either engage the other person or get hung up on. Don’t squander that with time-wasters like “How are you?” or “Is this a good time to talk?”

This may seem like you’re being polite. But in reality, you’ve wasted precious seconds asking a complete stranger a question to which he or she will feel obligated to respond in kind—when they really don’t care. The most polite thing you can do is get directly to the point.

6. Call More Than Once

Only a small percentage of your calls will result in reaching a live person. Unless you call back every few days or so, you won’t reach enough people to make your efforts worthwhile.

Be strategic. If you were to make 1,000 calls in a month, you’re better off calling 200 people five times rather than a thousand people one time each.

7. Prepare to be Rejected

When Kalanick began calling limousine companies to pitch the Uber concept, a third hung up before he even got to the core pitch. Another third hung up after about a minute and a half. But the third that were interested and wanted to meet helped launch his company.

Kalanick shared his early startup experiences at the Dreamforce 15 conference in San Francisco. You can hear his comments about cold-calling at the 13-minute mark:

Update: Uber’s valuation as of August 2018 is $72 billion.