Recently, while booking holiday travel, I discovered I had enough frequent flier miles to redeem for a round-trip ticket. I’m not really sure how I earned so many miles on one carrier, since my usual strategy is to fly whichever airline is cheapest. According to experts on the topic, I’ve already violated a few important rules of frequent flier mile redemption — know how many miles you are earning and make sure you redeem them.

For Delta customers in particular, Jan. 1 brings a host of changes to the carrier’s frequent flier program. The changes — announced earlier this year — include fee based rewards, a recently reversed decision to limit partner transfers, and the introduction of new redemption levels — none of which have been very popular with travelers.

Other airlines are merging or changing their programs as well, so here are a few things to consider when you are redeeming frequent flier miles for travel:

Don't wait: ThePointsGuy.com blog said it best this time last year, "If the past year has taught award travelers anything, it's that points and miles don't make very good long-term investments." Programs can change the process for earning or redeeming miles at any time which can subsequently change the value of miles you have.

Comparison shop: Don't assume you are better off cashing in reward points to fly. Check the actual price of travel and compare it to the points required. Divide the cost of a ticket by the number of miles that would be required for the same trip and multiply by 100. A rule of thumb offered in a recent issue of Consumer Reports magazine suggests that if it the result is more than one cent per mile, you should use frequent flier miles. Anything less, buy the ticket.

Book early: Consumer Reports also analyzed several frequent flier programs and found that Jet Blue, Southwest and US Airways significantly increased points needed to book at the last minute. Only United tended to lower the mileage requirement closer to the departure date. Booking three months in advance saved thousands of frequent flier miles on several major carriers.

Carefully consider credit: One route brand loyal travelers may take to help them accumulate points faster is to get a credit card. You can earn bonuses, upgrades and additional miles, but these cards aren't for everyone. Robert Semrad, Senior Partner at the DebtStoppers Law Firm of Robert J. Semrad & Associates, LLC offers this example: For one airline, it takes 75,000 miles to earn a round-trip ticket from Chicago to Arizona. To reach that mileage level, the credit card holder would have to spend about $35,000 in one year. Assuming the credit card holder only pays off $1,500 of their balance each month (with the average APR rate of 23.23 percent), they would be paying about $1,922.13 in interest for the year. The cost of the round trip plane ticket from Chicago to Arizona costs $1,284, meaning they spent an extra $683.13 to earn a free flight and they have an outstanding credit card balance of $18,764.62 to pay off. Bottom line, if you don't pay off your credit card bills in full each month, this may not be a good move for you.