You’re starting a new business but you don’t know everything there is to know about it. (Really, you don’t). If you’re smart you’ll find someone who does and try to absorb as much as you can.

That’s what Greg Selkoe did 12 years ago when he was dreaming up Karmaloop, a site that sells hoodies, sneakers, bags, and the like to young and techie trendsetters. He ended up snagging Sam Gerson, a retail expert who had been CEO of Filene’s Basement and president and COO of The Gap.

“I went to see him at his office and he took a look at what we were doing and he basically told me I was going to get ‘my (expletive) head handed to me’ and that I had no clue what I was doing,” Selkoe recalls. “But he said, ‘I’ll tell you what kid, I like your enthusiasm. Come see me once a week for an hour or two and I’ll meet with you.’”

Selkoe jumped at the chance and credits Gerson with teaching him—through these weekly meetings over the course of several years—how to do things like buy inventory, take markdowns, and manage payables.

“He didn’t ask for anything in return,” Selkoe says. “I wound up giving him a nice piece of equity in the company but it wasn’t something that he asked for. And he was someone who really enjoyed being back in the start-up world and working with young people.”

Later Selkoe also landed Frank Estey, one of the founders of Marshalls department stores, as an investor and advisor. “He really trained my buying team and I bounced almost every important decision off him."

Selkoe says the advice Gerson and Estey gave him was invaluable and much of the reason his company is such a success today. Last year Karmaloop generated $130 million in revenue.

Want that kind of success for your business? Then get yourself a good mentor, Selkoe says. Here’s his advice on how to do it:

Just ask.

Find and approach the person you want—even if it's a very successful business person. Some of these people speak at conferences, which is a great opportunity for approaching them. The fact is that even if they’re very busy some of these people are accomplished because they want to continue growing, learning and helping others. But be realistic: There’s a good chance they’ll say no. In that case...

Ask again.

You might not get an immediate response. If you reach out on LinkedIn, for example, it might take a few messages before a busy CEO volleys back.  Be persistent.

In fact, Selkoe didn’t get a meeting with Gerson right away—and that’s in spite of the fact that Gerson was the father-in-law of one of Selkoe’s friends. “He was a very hard guy to get in touch with. I think he thought he was [only] going to spend an hour with me and give me some advice. Even though he wasn’t that impressed with the condition of the company, he was impressed with my enthusiasm and creativity and I sucked him in, so to speak,” Selkoe says.

The key is getting the door open.

Stroke the ego.

In addition to touting the merits of your start-up, explain why you want him or her, specifically, to mentor you. What do you particularly admire or respect about the person?Everyone in the world likes their egos to be stroked. And tell them that you would love just five minutes of their time every once in a while.

Admit you don’t know everything.

Mentors appreciate those who have an authentic desire to learn. “If you’re five years in and you still don’t know [what you’re doing] something’s wrong but when you’re getting started in a new business I think people respect you more if you don’t try to fake what you don’t know but actually want to learn from other people’s experiences,” Selkoe says.

Don’t get discouraged.

Entrepreneurs need to be good at asking for all kinds of things, including help, money, and advice. They do this over and over again. Get used to it.