Over the past year, I've visited 8 different countries, half of which I paid for my flights using airmiles. Here are a few useful tips for building up your air mileage for free.

There are many ways to earn air miles for free, and some of the best ways don’t require you to change your buying habits at all. So let’s start off with the most lucrative option, credit cards.

#1 Airline credit cards

The quickest way to build a massive…