This article originally appeared in Inc. If you like this article,

• Click here to download Peter's FREE eBook, 5 Essential Steps to Growing Your Business with Millennials.

Tom Black is a serial entrepreneur, sales guru, and the go-to wine connoisseur for some of the biggest names in Hollywood. His list of financial and business successes would impress even the most diehard entrepreneurs; but what's truly impressive is that he started out living in a railroad boxcar.

Yes, you read that correctly: he and his family grew up making a home out of an abandoned boxcar. But what's even more compelling is how he turned a door-to-door book selling gig into billions of dollars in revenue over the course of his career.

As a Millennial entrepreneur, I admit that it's easy for me to assume that today's best sales require Facebook algorithms, search data and niche marketing funnels. But after talking to Tom, I realized that sales -- i.e., persuading someone to purchase what you're offering and what they need -- has perhaps no better training ground than a humble, door-to-door effort.

In fact, I was surprised to learn that the founders of Boston Consulting, Bain Consulting, and other high-profile executives sold books in the exact same company as Black, making it clear that these three steps comprise a universal system for scaling your sales regardless of what industry you're in.

Black's simple method of selling has three critical steps:

1. Quality of Prospect

There are three aspects to the quality of prospect. First, that you meet with decision makers; second, that they have the budget that your product or service requires; and third, that you either have a relationship with them or that you rapidly develop a relationship with them.

The last point is critical, because your success as a salesperson will depend on you rapidly warming up cold leads. For this, Black recommends using referrals and names to gain credibility.

Black gave an example from his youth: "The first summer I was selling books, I explained why I was there, and asked if I could come in. The last summer, I made it more relational by bringing into the conversation a prospect's sister's name, their preacher's name," and other data points that would anchor the prospect to Black and build instant rapport.

The key question for cold-selling is, "did you maximize the commonalities of the relationship?" If not, it's time to rework the sales pitch.

2. Quality of Presentation

If we were going to advertise one of your businesses, Black explained, "You could speak off the cuff without any preparation and use that for an advertisement. Or, we could hire professional actors, get scripts, film it until we got it perfectly and use that as an advertisement. Most prudent businessman would choose the second option."

And yet, Black pointed out that the majority of salespeople shoot from the hip when it comes to sales presentations.

When you plan what you're going to say, practice, and build a presentation based on sound communication principles, that will resonate far more with a prospect. "Everything we talk about in selling -- enthusiasm, asking questions, finding need, bringing people to point of decision, answering objections -- that fits into the quality of the presentation," making it one of the most important features of any sales system.

3. Quality of Effort

The last step is one that many sales teams fail to deliver; and yet, it's arguably the easiest step to execute on. Black defines quality of effort as simply how many people you see. "Two brothers follow each other in selling," Black explained, "Seymour and Sellmour!"

When it comes to selling, the law of averages truly is a law; Black drills into his sales teams that sales and advertising are the gas and oil of the free market enterprise, and both are based on the law of averages.

"When you're in a slump," Black warned, "see more people. We have a natural tendency to slow down and focus on our current prospect list when we're in a slump, but in reality the best thing to do is see more new people."

True salespeople like Black know that selling is systematic, and not the outcome of voodoo magic, hopes and dreams. While he's not building his famous wine collection, he's teaching the proven sales system to the next generation of business leaders who want to scale their enterprises in our cluttered, modern world.

Who would have thought that the best sales strategy today is still the oldest one in the book?