6 ways to earn extra frequent-flier miles

Check out all offers carefully before signing up for any frequent-flier miles programs. Remember, a free ticket may mean inconvenient travel times or days.

"It is easy to earn miles, the problem is on the redemption side," says Winship.

For example, there are capacity controls on every airline, meaning that there will be limited seats available when redeeming frequent-flier miles.

"This does detract from the value of (frequent-flier programs)," says Winship.

Also be aware that frequent-flier programs have recently come under government scrutiny for failing to honor miles. In November, Sen. Charles Shumer, D-N.Y., called for the Department of Transportation to look into complaints from frequent-flier program members regarding expired miles.

Finally, Steiger warns that deals come and go quickly. Grab them while they are available and keep your eyes peeled for new deals.