I'm sure most of you already do this, but I'm going to preach for a minute anyways. Please check your credit card statement at least once a week, especially around the time a payment is due.
Since we were on vacation, I paid my credit card online this month. I had two payments posted and just waiting to be applied to my credit card. Well, for some reason they were not applied to my account until after the payment date, so I was charged a late fee.
Thankfully I was checking my credit card statement, so I got on the online chat with a representative and they cleared up the problem immediately.
If I didn't check my card regularly, I wouldn't have noticed this mishap until I got my statement in the mail later in the month. Then, it would have been harder to straighten out.
So, moral of the story: Check your credit card statement online weekly!