Unless you work as an international courier, your ability to accumulate frequent flier miles in the air is pretty limited. The fastest way to rack up the miles needed to reach free flight award levels is by using one mileage-earning credit card and charging everything you buy on it: gasoline, groceries, meals, subscriptions, dues, doctors office copays. When presented with any bill, your first question should be, May I pay with my credit card? I once paid a $12,000 bill for a semesters tuition at a college in Australia with a credit card, earning in that one transaction half the miles needed for a free domestic flight. Theres a huge caveat here, however: You have to pay your credit card bill in full and on time every month; otherwise, late fees and finance charges could easily negate any airfare savings. When it comes time to redeem miles, plan well in advance, be flexible with dates, and choose long-haul flights. My biggest score was three round-trip tickets from Boston to Honolulu at a time when the lowest rate was nearly $1,000 a ticket. We had a terrific time in Hawaii and, yes, we charged everything.