11 things to do in your 20s to become a millionaire by 30

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"In a free-market economy, anyone can make as much money as they want," emphasizes self-made millionaire Steve Siebold, who has also studied over 1,200 of the world's wealthiest people.

That applies to 20-somes.

To help you reach the seven-figure mark by 30, we rounded up 11 pieces of advice from people who became millionaires at a young age and people who have studied hundreds of self-made millionaires. We can't guarantee millionaire status, but doing these things won't hurt your odds:

1. Focus on earning

"In today's economic environment you cannot save your way to millionaire status," writes Grant Cardone, who went from broke and in debt at 21 to self-made millionaire by 30. "The first step is to focus on increasing your income in increments and repeating that.

"My income was $3,000 a month and nine years later it was $20,000 a month. Start following the money, and it will force you to control revenue and see opportunities."

Earning more money is often easier said than done, but most people have options. Read about 50 ways to bring in additional income, some high-paying jobs you can do on the side, how you can earn passive income, and the first step to take before starting any business, from an entrepreneur who earns up to $170,000 a month.

2. Develop multiple streams of income

One way to earn more is to increase your streams of income.

In author Thomas C. Corley's five-year study of self-made millionaires he found that many of them develop multiple streams of income: 65% had three streams, 45% had four streams, and 29% had five or more streams.

These additional streams include real-estate rentals, stock market investments, and part-ownership in a side business.

"Three streams of income seems to be the magic number for the self-made millionaires in my Rich Habits study, but the more income streams you can create in life, the more secure will your financial house be," he writes.

3. Save to invest, don't save to save

Writes Cardone:

"The only reason to save money is to invest it. Put your saved money into secured, sacred (untouchable) accounts. Never use these accounts for anything, not even an emergency. This will force you to continue to follow step one (increase income). To this day, at least twice a year, I am broke because I always invest my surpluses into ventures I cannot access."

Investing is not as complicated or daunting as we make it out to be. The simplest starting point is to contribute to your 401(k) if your employer offers one, and take full advantage of your company's 401(k) match program — which is essentially free money — if it has one.

Next, consider contributing money toward a Roth IRA or traditional IRA, individual retirement accounts with different contribution limits and tax structures — which one you can use depends on your income. If you still have money left over, you can research low-cost index funds, which Warren Buffett recommends, and look into the online-investment platforms known as "robo-advisers."

The key to consistently setting aside money is to make it automatic. That way, you'll never even see the money you're contributing and you'll learn to live without it.