Frequent flier miles can be contentious beasts—the kind of thing that divides marriages, or prompts travelers to keep Scrooge-like hoards that then vanish (along with the airline). 

People have opinions, and loyalties—though not all programs are created equal. You're in good shape if you have miles with United, Delta, American, or Alaska; they all have multiple international partners you can leverage to your advantage. Virgin America, Southwest, and JetBlue offer fine programs, too, though they're typically more useful for free tickets within North America. Tempting, but you'll get more out of your miles flying to Hong Kong and London—and if you have enough miles, you'll get an even better deal if you redeem for first or business class, tickets that ordinarily might cost $5,000 or more.

That's just one trick savvy travelers should know. Here are nine more tips for getting the most out of your miles.