If you're going to take personal finance advice from anyone, you can't do much better than Mark Cuban. The Shark Tank shark and Dallas Mavericks owner sold his first startup to CompuServe in 1990 for $6 million. Then he sold his second business to Yahoo for $5.9 million in 1999. Since then he's started or acquired several other businesses and invested in many more. His current net worth is estimated at about $4.2 billion. 

For someone who's gotten extremely rich taking risks on a lot of investments, Cuban has some surprisingly down-to-earth advice to share. The personal finance site GOBankingRates has carefully reviewed Cuban's book, blog, and interviews, distilling out 20 pieces of financial advice he's offered over the past few years. You can find the full list here. These are some of his best tips.

1. Start by paying off all debt.

"The best investment you can make is paying off your credit cards, paying off whatever debt you have," Cuban said in an interview with MarketWatch. "If you have a student loan with a 7 percent interest rate, if you pay off that loan, you're making 7 percent, that's your immediate return, which is a lot safer than picking a stock, or trying to pick real estate, or whatever it may be."

Credit cards, of course, have a much higher interest rate, so there's an even bigger benefit in getting them paid off. "Using a credit card is OK if you pay it off at the end of the month," Cuban told an interviewer from Money. "Just recognize that the 18 or 20 or 30 percent you're paying in credit card debt is going to cost you a lot more than you ever could earn anywhere else." For debt that can't be quickly paid off (a mortgage or student loan, for example), he suggested taking advantage of low interest rates during economic down times to refinance.

2. Save six months of income.

You should try to save up six months of income and keep it available, Cuban told Vanity Fair. "If you don't like your job at some point or you get fired or you have to move or something goes wrong, you're going to need at least six months income," he explained.

3. It's OK to make risky investments, but they should be only 10 percent of the total.

Self-made millionaires and billionaires got there by taking calculated risks, Cuban acknowledges. So investing in something completely risky is just fine -- so long as you limit it to only 10 percent of your overall investments. "If you're a true adventurer and you really want to throw the hail mary, you might take 10 percent and put it in bitcoin or Ethereum, but if you do that, you've got to pretend you've already lost your money," Cuban said in that same Vanity Fair video. "It's like collecting art, it's like collecting baseball cards, it's like collecting shoes." In other words, "It's a flyer, but I'd limit it to 10 percent." 

What should you do with the other 90 percent? Put it into the cheapest index fund tied to the S&P 500 that you can find, he says.

4. Shop for discounts.

Is this really personal finance advice? Yes, Cuban says. It's tough to make a high rate of return in today's investment climate, so you could be better off, say, buying two years' worth of toothpaste if you find it at 50 percent off. 

"Saving 15 percent on $1,000 worth of items you know you will absolutely spend money on is a better return on your money than making 15 percent in a year on a $1,000 investment, because you don't pay taxes on it," he explained in a blog post. 

You don't really think of bringing home bulk items from Costco in the same way that you do putting money into a mutual fund. But look at it the way Cuban does, and suddenly it makes perfect sense.