I've never had too many problems with my credit score except for two extremely dumb things.
During college I lived in a house with roommates. We all were responsible for one bill that we had to open under our name, so I got the cable bill.
We paid on time and all that good stuff. When the school year ended, we went our separate ways and I moved into an apartment. I never bothered to look at my credit score.
Two years out of college I decide to check my score and report and see a cable bill in collections for a measely $52! It was one of those balances that lingered after we assumed we had paid the final bill.
My credit score was in the 600's. I called the collections agency and paid it off right away. Contacted Experian and told him the bill was settled and my score improved.
Another dumb thing that gets me is I applied for a bunch of credit cards in college including a Capital One card with a credit limit of a whopping $300. Yes dumb old me forgot about a small balance or ignored it (shame!) and didn't pay for it for 60 days! So there's a little red on my report.
DUMB DUMB DUMB!
Well as of this year I started at 712. I closed a few store cards, okay more like 4 of them (Macy's, Target, NY&CO, Kohl's) and it improved my score because I improved my open credit card utilization AND the average age of my credit lines got older! Yes I know. So now I'm at a 762!
I highly recommend Credit Karma for your free credit score (www.creditkarma.com). Yes there are a lot of advertisements, but they're pretty useful if you're shopping for financial products.