The average household active in a rewards program earns $622 a year in rewards points or miles, but doesn't redeem $205 of those earnings, according to a study last year from Colloquy and Swift Exchange. Credit card issuers are pocketing nearly a third of customers' earned rewards.

"There are probably a slew of people out there who have cards with points on all of them," says John Ulzheimer, the president of consumer education at SmartCredit.com. "And they don't even realize it."

Of course, the point of getting a rewards credit card is to treat yourself to the perks of the rewards program. The best way to make sure you get the most out of your rewards credit card is to pick the right one, use it to your greatest advantage and avoid possible pitfalls such as leaving points on the table.

Picking the right rewards credit card

The first hurdle is to make sure the credit card and rewards program you choose fits your financial lifestyle. If you travel a lot in your free time, maybe a hotel or airline card is a good fit for you. A gas rewards credit card might be best for a road warrior.

But Ulzheimer, among other consumer advocates, recommends a cash-back card because of the flexibility and simplicity of those programs.

"Cash has no blackout dates. You don't have to work with a third party," he says. "And we all understand the value of a dollar versus the value of an airline mile."

Additionally, many cash-back cards come with numerous ways to redeem your rewards aside from just cash. Some allow you to redeem for a statement credit, gift cards or charity donations.

Not all cards are created equal, though, even if they offer a similar type of rewards program. That's why it's important to read the fine print.

Know the rules

Rewards credit cards come in many flavors. Some require a certain amount of spending before you can earn rewards. Others cap the amount of rewards you are able to earn. In addition, you may find some cards have blackout dates for redeeming travel-related rewards or expiration dates on points.

"These rewards programs also are subject to change at any time," says Linda Sherry, director of national priorities at watchdog group Consumer Action.

Cash-back cards can also involve a little advanced planning. While most cards offer 1 percent to 2 percent cash back, in some cases consumers have to hit an annual spend threshold to earn the rewards, says Lisa Hronek, senior analyst at Mintel Comperemedia.

Some rewards credit cards cap how much you can earn in different categories, while others only allow you to rack up points in specific categories such as dining, gas or groceries. Also, find out if you need to register your credit card online to get the maximum cash-back bonus.