If, however, most of your miles will come from paid tickets, then it is important to choose a frequent flyer program with an airline within an alliance you will use most frequently. Remember you must have a minimum of 20,000 or 25,000 miles before you can receive any round trip award with most programs. There are several considerations for choice of airline program:

There are three major worldwide alliances of major airlines - Star Alliance, One World, and Sky Team.

• If you earn flight miles from paid flights on any airline within an alliance, you may credit them to any airline within that alliance. So for starters stick with one airline within each alliance for crediting your flight miles. Pick the one from which you can get the most non-flight miles (for credit card or brokers bonuses, for example).
• You may use miles from any one airline within an alliance to get tickets on any combination of airlines within that alliance. For example, I flew within the Star Alliance network from San Francisco to Korea on United Airlines, stayed overnight, then flew from Korea to Bangkok on Thai Air, toured Vietnam from there for a few weeks, then returned from Bangkok to Tokyo on Thai Air, stayed there four days, then returned to San Francisco on All Nippon Air - all in business class, all for the United Airlines miles price of one round trip to Asia. But you may not combine miles from more than one airline to get an award ticket. This why I say to start with one airline within each alliance for miles accumulation.
• Star Alliance is the largest. It is the easiest alliance from which to get an award ticket, because it has the most flights to most places. United and Continental Airlines (these will merge by December 31, 2011) and U.S. Airways are the three U.S. based airlines within this alliance. Note that you may use the miles of any of these three to get a flight on any other. This makes this alliance extremely useful for flights within the U.S. Click my link to see the list of non-U.S. based airlines that are in the alliance. My favorites (as of 2011) include Lufthansa, Swiss Air, and Singapore Airlines. I would chose to fly any of these three in business class over any U.S. based airline's business class.
• The second largest alliance is One World. American Airlines is its only U.S. member. Click my link to see the large list of non-U.S. based airlines that are in the alliance. My favorites (as of 2011) are Cathay Pacific, Japan Airlines, and Lan. British Air is a member, but beware of its infamous very high "fees" for award tickets.
• The third largest alliance is Sky Team. Delta Airlines is its only U.S. member. Click my link to see the list of non-U.S. based airlines that are in the alliance. My favorite (as of 2011) is Air France, a comfortable way to get to Europe in business class.

Some airlines are not part of any alliance, but have a useful set of partners.

• The Alaska Airlines program is one of my favorites due mainly to its partners, including (as of 2011) Delta, American, British Air, KLM, Cathay Pacific, Air France, Qantas, and Lan. In 2011, for example, the "fees" for a round trip business class award ticket between San Francisco and Bangkok (via Hong Kong) were hundreds of dollars less than the same award ticket from British Air. Note how the partners span several of the major alliances. Alaska usually has a different inventory of award tickets from a particular airline than does that airline or any within its alliance. That is a very valuable flexibility when you are looking for such a ticket. However, Alaska requires that you fly your entire trip on the same airline, and can be quite restrictive about layovers and open jaw tickets.
• Taca is my favorite airline for getting around Central and South America. They treated me extremely well when I was in Machupichu on 9/11/2001. Their help desk at their San Jose, Costa Rica hub has to be one of the best in the world. (However, their service at San Francisco International Airport has be one of the worst.) It's U.S. partners in 2011 were United and Continental - a very good reason to accumulate miles with those two. At that time they partnered with several Latin American airlines, and a couple of European ones. I don't know whether or not they allow multiple airlines on the same ticket.

Different programs require different numbers of miles for awards. I could have paid 35,000 or 50,000 miles for my trip to Peru, depending on the airline. So if you know where you want to go, choose your program accordingly.

Most airlines mileage programs cause your miles to expire under certain conditions. Most US airlines miles expire in one to two years of the last mileage adding activity (so it is easy to maintain those miles forever), but some U.S. airlines (like Delta in 2011) do not expire your miles. (But that may change at any time.) Southwest, AirTran, and some of the other low cost domestic airlines expire your credits after a year or two of earning them, so with these airlines you have to be sure you can earn enough credits to get a ticket and can decide what ticket you want within that time period. Many foreign airlines expire your miles after a certain time, regardless of activity. If you need an activity to keep your domestic airlines miles alive, one of the easiest is through Rewards Network (iDine), a program described on my Other Programs I Like page in the dining section.

It usually costs you most of your miles if you try to exchange them between airlines -so don't plan on doing this. Just follow my What's New page to accumulate as many miles as you can on lots of airlines within all the alliances, so you will always have enough for your needs. Webflyer maintains and excellent mileage converter page on exchanging miles between airlines and/or points programs. Always use this tool before converting hotel or Amtrak points to miles.

To sign up for a mileage program, first check my Airlines Registrations Bonuses section of this web site to see if you can get miles for joining the program. If you can't, then go the airline's web site and navigate to the online registration form. To find the web site, just use your favorite search engine.

The airlines' sites also give all details need about their frequent flyer programs, including partners, expiration policies, and how many miles it takes to get to where you want to go. Be sure to sign up for emails from airlines of interest. These are a major source of the deals I post on this website.

Even though you have already purchased your ticket, it is not too late to receive miles for it. Just sign up for a miles program, call the travel agent or the airline reservation number and give them your frequent flyer number, and when you show up at the gate, ask them to check to be sure the number is in your account. Even if your miles are not credited, perhaps even if you were not a member of the program at the time of your flight, you probably can still get them by sending in your boarding pass receipt. Always save that receipt, for lots of reasons, including getting miles credit.