Don't consent to overlimit fees
The CARD Act mandated issuers to get customers' permission to allow them to go over the limit -- and rack up fees of up to $35 in the process. Fortunately for consumers, banks haven't (yet) rolled out the kinds of aggressive campaigns they've employed to get customers to enroll in overdraft programs for checking accounts. Banks says the easiest way for consumers to avoid this fee is to not sign up for it in the first place.
Giving the issuer permission to let you exceed your credit limit not only sets you up for a fee, but it also can have negative repercussions on your credit score. A full 30 percent of your FICO score is based on amounts owed, part of which comes from credit utilization, or how much of your available credit you've used. If you exceed your limit, you've effectively gone "upside-down" on that ratio, which reflects poorly on your score.