Not that this is the most important, but it is the first one I can think of (seeing as it just paid off for me in a great way). I was able to book my one-way flight to Atlanta for $140 as opposed to paying the outrageous price of $557. This advice might not be as applicable outside of the US, but since we don’t have the concept of budget airline (Southwest can kiss my ass, AA is cheaper or the same price for every flight I’ve tried to book there) it is a good way to get rewarded for flying.
Living in DFW, I joined the American Airlines AAdvantage program when I first started traveling. I chose AAdvantage because the hub for American Airlines is DFW, which means they have a bajillion flights a day and they fly direct to most places I wanted to go (i.e. London, Paris, Sydney). Dad traveled a bunch for work, and he earned so many air miles and got to go on heaps of vacations for stupid cheap (like he and Mom went to Hawaii for like $200 for the two of them, plus they were offered to upgrade to First class at check-in for $15 each). My first trip abroad (which was, coincidentally, my first time on an airplane) was to Australia when I was 13 and I got bit by the travel bug big time. I worked from the time I was 16 at various restaurant jobs and saved up enough money to plan my next trip abroad. Stocking up air miles was by far the best choice I’ve made when it comes to saving money on travel.
It doesn’t really matter which airline you choose, just pick one that you are actually going to use. If you travel internationally, make sure you check out the partner airlines and the rules for earning miles on their flights. You’ll earn miles for every trip you take and eventually you’ll end up with enough miles to fly for free. It took me quite a few trips to get a nice balance, but the miles you’ve earned don’t expire as long as you make another flight within 18 months (for AA). There also have it so you can earn miles via the credit card associated with the program and you can register your card details (or enter promo codes) to earn points shopping online at some places.
Rambo has flown back and forth from Scotland to DFW so often that he’s got heaps of miles and flew us to NYC for $150 total last summer. For my trip to Vienna, I had to buy a couple thousand miles (which were reasonably priced) and flew there for less than $500. Fronzel, who uses a different airline, flew himself and M.Stewart to Fiji and New Zealand for almost free thanks to air miles he’d racked up.