How long do you have before your accounts expire? That will depend on what you do to earn the miles. If they're fast approaching, the quickest way would be to purchase miles or make a redemption for something. Dining for Miles would be an easy way as well if you don't have any hotel stays, car rentals, etc., coming up. Or, you could sign up for
e-rewards or
e-miles, too. They make take a bit longer to accumulate miles but are fairly painless, however like Jazzop mentions, you can only dump miles into a single account - so e-rewards could be NWA and e-miles for Delta, for instance.