It is certainly not an easy feat. Only a tiny fraction of American workers have been able to amass $1 million or more in their 401(k)s and employer-sponsored retirement plans, according to the Employee Benefits Research Institute.
The average 401(k) account balance is just shy of $59,000. Yet whether you have saved $50,000 or $5 million, some secrets of the rich can be very instructive when it comes to building your own retirement fund.
(Read more: Questions to help protect your retirement savings)
Fidelity, the nation's largest retirement plan provider, surveyed wealthy investors whose assets totaled more than $5 million on average, including at least $2 million from employer-sponsored retirement plans. Here are some common trends:
There is often another simple strategy at work too: Don't spend more than you can afford.
(Read more: What you should be asking your financial advisor)
"Most millionaires accumulate their wealth because they didn't spend it," said certified financial planner Barry Glassman, founder and president of Glassman Wealth Services in McLean, Va. "Given the fact that they're able to plan, think longer-term and live within the means—and that's the most important thing—they're able to accumulate more wealth over time."
There are some differences, though, between older millionaires and younger generations.
Fidelity found boomer millionaires, who are 49 years old and older, are more likely to stick with the same old investment strategy. Four out of 10 boomer millionaires did not add any asset classes in the past year. Meanwhile Gen X and Gen Y millionaires, who are 48 years old and younger, are more willing to make changes and add more complex investments, such as foreign currency, international individual securities, venture capital and derivatives, to their portfolios.
(Read more: Retiring with more: Don't wing it on your 401(k))
Still, careful planning comes first. It is an essential building block at any age.
That's what younger millionaires do—even though retirement may be decades away. "Because they're planning, they're diversifying, they're thinking long-term," Glassman said. "And that's what's allowing them to take additional risk in places where it's prudent."