ATLANTA -- Many Americans have two, three or more credit cards in their wallets but most cardholders are probably not getting paid to use their cards.

Joe Leader is much more than a frequent flier. He's a walking advertisement for what's known as affinity or reward credit cards.

"I've gotten over 200 free tickets on AirTran (from) flying with them and using the AirTran Visa," Leader said.

Airline reward cards generally provide one mile, or point, for each dollar charged to the car. Some cards even double the mileage on things consumers routinely buy, like gas and groceries.

Consumers who use cash rebate cards should pick a low or no fee card that has the highest refund rate. Consumers should also watch out for cards that cap, or limit, the amount of earnings in one year or boost the reward if you carry a balance.

Clark Howard Web Sites Consumer Credit Counseling Service Card Ratings.com Card Web.com Bank Rate.com

"Any place that takes a credit card, I always use a credit card," Leader said. "That's because the best strategy is to use these affinity cards and pay them off every single month."

There are three rules for using reward cards.

• Consumers earn more by charging more.
But the consumer must be able to afford the payments when they come due. Of the 700 plus credit cards offering rebates and rewards, almost all share one thing in common:
"Generally speaking, the rebate cards have higher interest rates," said Curtis Arnold, who runs a Web site that compares credit card offers.
"If they don't pay off that card or cards in full every month, then reward cards are not where they need to be looking."
• Consumers should know their interest rates.
Arnold looks at thousands of offers on Cardratings.com.
That Web site, along with Cardweb.com and Bankrate.com are places where consumers can log on and compare credit cards in terms of interest, rates, fees and rewards.
Brad Thompson studied the fine print and discovered that charging his gas would help him earn a trip for two to the West Coast during the Christmas holidays.
"Gas, groceries, anytime we go to Lowe's, restaurants, and day-to-day spending, we (purchase with) a card," he said.
But he actually breaks rule 3.
• Avoid annual fees.

Thompson pays the yearly charge but believes the rewards far outweigh any cost.

If you are a consumer who has good credit, make companies pay you for your business. Charge everything to earn more but always pay it off. And pick cards with low interest and low, or no, annual fee.

On Tuesday's report, Clark Howard shows you how to beat credit card companies at their own game, which is to keep consumers deep in debt.