First, the bad news. To qualify as a millionaire in the United States today, you need to earn approximately $4m (£2.4m). Thanks to taxes, $4m whittles down to $1m before there is time to add it up. But here is the good news. Earning $1 m, $4 m, even $50m, is as simple as baking a three-layer cake. According to Dr J Thomas Stanley, a marketing guru who studies millionaires for a living, there is no need for quiz shows, wealthy parents or a Harvard MBA to get you into the club. In fact, you don't even need an A-level.

What you do require is the recipe for achieving wealth. Stanley claims to have formulated one, which he has published, after a study of 1,300 self-made American millionaires. He calls this recipe, and the eponymous book, The Millionaire Mind. This is a state of being and a career that consistently trumps shortcomings in intelligence or connections, a mindset guaranteed to earn you a fortune.

The crux of his findings is that hard work, focus, goal-setting and discipline are the direct path to riches. Understandably, the idea that a rigorous work ethic, as opposed to an Oxbridge education or mummy and daddy's money - is what it takes to make millions has been greeted with delirious delight by Bill Gates wannabes.

Released in the US only three weeks ago, Stanley's book, The Millionaire Mind, is already number four on the New York Times bestseller list. "What I found, consistently, is that of all the factors involved in financial success, hard work was first, and graduating at the top of the class ranked last," says Stanley, who lives in Atlanta. "Most millionaires made Bs and Cs at university. But education is such a major issue in America. Parents get hysterical if their children don't get As in kindergarten; but I found a high IQ is no indicator of success. Millionaires build empires on creativity and common sense."

The millionaires Stanley studied had an average net worth of $9.2m (£5.5m). The majority were entrepreneurs and 73% were described as academically average. He also found that they were not motivated by money or dreams of yachts in the Greek islands and castles in Marbella. "Self-made millionaires do not look at money as a goal in itself. Ninety per cent told me their objective in starting out was to be independent, to follow their passions, to control their lives."

So if intelligence, degrees, quiz shows and lottery winnings don't count, what does? Stanley sums it up neatly: "First, millionaires choose a career in an area that matches their talents and interests. This ensures they are always motivated to work harder and longer than anybody else.

"Then they consistently think outside the box, seeing opportunities others have ignored. This is exactly what Richard Branson did with Virgin. He really is my hero. He consistently thinks outside the box to expand his empire."

Consider also the case of Donald Sonner, the 64-year-old head of the Southern Bloomer Manufacturing Company in Tennessee, one of the millionaires Stanley interviewed. Sonner only completed one year of high school but was a millionaire by 24. He uses scrap cloth discarded by garment manufacturers to make underwear for prisons and gun-cleaning patches. "Mr Sonner got rich by working hard and coming up with an idea nobody else had," says Stanley.

The trick is to pick a career wedded to your interests, think laterally, then pair those elements with a disciplined work ethic. Stanley emphasised that all the millionaires in his survey set high goals and then worked around the clock to meet them. "Millionaires say they work harder, place a high priority on honesty and integrity in business, and are prepared to take financial risks. They draw up plans and constantly evaluate them. They never lose sight of their goal."

They also use time efficiently. Another millionaire Stanley interviewed was a Mr Benjamin, a school-bus driver who spent all his work breaks studying the stock market instead of messing about with his friends at the bus station. He began investing tiny amounts, taking risks and rolling with the punches when stocks took a tumble. He retired after 20 years, worth $3m.

"It's all about focus. Millionaires make a decision to tune out everything else and concentrate on one thing, be it creating a retirement fund, or launching a record label. Mr Benjamin focused on investing, schooled himself, and took calculated risks that paid off."

In New York, where there are said to be 30,000 millionaires, all the talk is of Joseph Park, 28, who quit his well-paid job as a Wall Street trader to launch www.kozmo.com, a company that delivers goods to your home within an hour of you emailing an order. Analysts dismissed the idea as unworkable and Park was warned that he might be headed for bankruptcy. But the public loved the idea, business is booming and last month Park raised $100m in venture capital. Stanley says Park is a perfect example of someone having a novel idea, laser-like focus, motivation, and the gumption to take a risk.

Stanley also found that psychologically, like Park, self-made millionaires were resolved to overcome predictions by school teachers or bank managers that they or their plans would not amount to much.

Many, he discovered, used negative criticism of their efforts and characters as a spur. "What is interesting is that many millionaires also had parents who never told them they would be losers if they didn't get into Harvard or Yale. They said you can do anything you want to, try everything. If you fail, keep going."

So where will tomorrow's millionaires come from? Contrary to conventional wisdom, they are not lining up at the trough of the internet. Park, he says, was one of the lucky ones.

In fact, Stanley's findings were that steel manufacturing, commercial equipment rental, dredging, mushroom-growing, outdoor advertising, commercial banking and construction contracting produced at least five times more wealth for their owners than for others in the same age and income brackets. "Sure, some new millionaires will come from the web, but you will always need food, clothing and shelter, and the person who has a new idea in those areas, who is disciplined and sets goals, will become a millionaire," he predicts.

Rich list

Stanley discovered that self-made millionaires:

* Choose their careers so they can take full advantage of their abilities and aptitudes.

* Understand that the key factors rewarded by the economy are integrity, discipline, hard work, leadership, a supportive spouse, enjoying one's career and focus.

* Have usually inherited less than 10% of their household net worth and 61% have never inherited, or received gifts of money.

* Live a comfortable but not extravagant lifestyle, with little or no debt.

* Take calculated financial risks and do not gamble.

• The Millionaire Mind is published by Andrews McMeel, $26.95. It is not yet available in British shops.