not checking your credit report for mistakes
missing even one payment
Missing a payment is one of the quickest ways to lower your credit score. And that's the case even if late payments don't become a pattern, says Beverly Harzog, a consumer finance analyst and credit-card expert at U.S. News and World Report. "Some consumers don't think that missing one credit card payment is a big deal," she cautions. "A payment that's only 30 days late can reduce your score by a substantial amount. And once that late payment hits your credit report, it stays there for seven years." According to FICO, that substantial amount can be as much as 110 points for someone with an otherwise great score.