The FICO credit score equation might be a black box, but there have been thousands of articles written about what you should and shouldn't do when it comes to your credit score. Most of them are pretty obvious--pay your credit card bills on time, don't apply for a lot of credit, and keep your nose clean. There are, however, a lot of weird ways you can hurt your score without you even realizing it. Closing Credit Cards. This has become less "strange" in recent years, but closing your credit cards...