Frequent-flyer programs are the heart of most airlines’ marketing efforts and have allowed thousands of travelers to enjoy free flights, first-class upgrades, and even entirely free vacations. In fact, so many freebees have been given away that the airlines have been reining in the rewards. But opportunities still abound, and the number of ways to earn miles has increased dramatically. If you pay attention to the programs (read the member bulletins!) you can capitalize on the frequent-flyer bonanza.

Concentrate Your Mileage with One Airline. Upper tier programs are becoming the focus of all frequent flyer programs, which have been trimming benefits for the least frequent flyers to enhance those of the most frequent, a sort of "We cheat the other guy and pass the savings on to you!" deal.

This puts travelers into two groups: those who fly in excess of 20,000 to 50,000 actual flight miles annually, and those who don’t.

Those who do get bumped into upper-tier programs dubbed Gold, Platinum, Preferred, Elite, Medallion, Premier, and the like. Program benefits include: greater availability of award and upgrade seats; priority boarding, waitlisting, check-in, and reservation lines; more ways and opportunities to upgrade; fewer charges for expedited award processing and ticket changes; and more bonus mileage -- in short, all of the goodies.

If you don’t fly 20,000 actual flight miles annually, you lose not only the fun perks, but possibly your mileage as well: Choose a program in which mileage for all members doesn’t expire after three years.

Claim Car and Hotel Bonuses.

Program affiliations allow you to earn bonus miles for hotel stays and car rentals; sometimes they don’t even require a flight in conjunction. At 300 to 1,500 miles for a single car or hotel transaction, you could earn more miles driving and sleeping than flying. Inside Flyer magazine (719/597-8880 or www.insideflyer.com) is a consolidated source for bonus opportunities for all major and most minor programs.

Claim Affinity Bonuses. You can earn money sending flowers, making long-distance phone calls, investing in money market funds, test-driving vehicles, subscribing to magazines, filling out surveys -- the list is almost endless. The most popular method is using a charge card, earning a mile or sometimes more for each dollar charged. If you’re charging at least $10,000 a year, you should definitely be using an affinity credit card.

Diners Club (800/2-DINERS, 303/799-1504 or www.dinersclub.com) has the most flexible program but it's not widely accepted beyond hotels, airlines and rental cars in most of the world.

American Express (800/327-2177, 910/333-3211 or www.americanexpress.com) offers Membership Miles on many of its cards, a special "Rewards Plus" Gold Card, with special benefits and increased earning opportunities for frequent flyers, and the Platinum and Centurion Cards, with an incredible array of benefits for luxury travelers and very frequent flyers.

Almost all airlines have an affiliated MasterCard/Visa program, but beware -- these cards have high annual fees and finance-charge rates. If you’re carrying a balance, you’re not a good candidate for these. Many MasterCard/Visa card issuers have their own travel reward programs that work well for those who want to redeem their awards only for free coach class tickets.

Book Award Travel Early or Late. Using your earned mileage is not always as easy as it seems. If you want to go to Hawaii or the Caribbean in the winter or Europe in the summer, you need to book almost a year in advance. Even then, you might not find your choice of flights available. Ironically, those same unavailable flights often become available closer to departure, as the airlines adjust their award inventory constantly.

This can be a benefit if you have to make a last-minute trip. Another good use of your miles is any trip that doesn't entail a Saturday night stay. Don't redeem awards when you could buy a comparable trip for less than two cents per award mile. If the comparable paid trip is worth more than five cents per award mile, you're getting a great deal.