The best way to earn air miles is by use of a credit card.
However if you don't have a credit card there are a few ways you can earn air miles without the use of a credit card such as through car rentals, dining programs, online shopping portals, hotel or motel stays, Taking Online Surveys, Sending Flowers and even Banking and Investing.
Sometimes you can earn air miles through your banking or investments as well so check with your bank to see if you qualify to earn air miles.
If you don't have a regular credit card then you might also try getting an airline credit card that you can earn airline miles through.