After people retire, running out of money is a constant worry. But by taking steps during your career to shore up your three key sources of retirement income, you can go a long way toward guaranteeing yourself a secure retirement.

In the following video, Dan Caplinger, The Motley Fool's director of investment planning, goes through the three keys to having enough retirement income: Social Security, pensions, and investment income. Dan notes that having a successful 35-year career is the best way to maximize Social Security benefits, but that many can also take advantage of other retirement-income opportunities. Pensions have become less common lately, but they're still available to some workers, and knowing how they work can help you make more from them. Finally, Dan notes that investment income plays a key role, discussing the role that 3M (NYSE:MMM), McDonald's (NYSE:MCD), Aflac (NYSE:AFL), and other dividend-paying stocks can play in building an income-producing portfolio.