"Be a smart shopper," Cuban tells CNBC Make It.
"You will quickly find that the greatest rate of return you will earn is on your own personal spending," he writes on his blog.
"Save your money. Save as much money as you possibly can. Every penny you can. Instead of coffee, drink water," he writes. "Instead of going to McDonald's, eat mac and cheese."
Cuban also suggests things like buying two years' worth of toothpaste when it's 50 percent off. "There's an immediate return on your money," he tells Vanity Fair.
Cuban's "Shark Tank" co-star Kevin O'Leary takes a similar tactic. He refuses to spend $2.50 on a cup of coffee.
"Do I pay $2.50 for a coffee? Never, never, never do I do that," O'Leary tells CNBC Make It. "That is such a waste of money for something that costs 20 cents. I never buy a frape-latte-blah-blah-blah-woof-woof-woof for $2.50."
He makes coffee at home, and puts his savings to work in the stock market.
"I drink coffee, one cup every morning," he explains. "It costs about 18 cents to make it, and I invest the rest."