January and February are typically the highest default months on car payments, says Eric Hoffman, spokesman for Aware, or Americans Well-informed on Automobile Retailing Economics, based in Washington, D.C.

Factor your potential monthly car payment into your budget, and don't forget to include those credit cards and holiday bills coming due in January and February. If you know you're going to pay hundreds or thousands of dollars during those months on gifts for your family and friends, you may need to adjust your down payment, buy a used car or a cheaper new car, or hold off on your purchase.

At the same time, you may see your monthly take-home pay drop during the winter, depending on how you are paid. "The last thing you want to do is to get stretched too thin," Hoffman says.