Credit score is a means to an end, not an end in itself
Other tips include not asking to have your interest rate lowered, and opening new cards.
Wisdom like this is a case of getting way too nerdy about credit scores, to the point where it actually becomes detrimental to your financial health.
I've never met -- or heard from -- anyone who used credit responsibly for a reasonably long period of time and didn't end up with a credit score high enough to buy a house with a decent-sized down payment. First-time home buyers can get FHA loans with credit scores in the 600s -- which is below average.
And remember: buying a house is really the only intelligent thing the majority of people will ever do with a credit score. Getting higher credit card limits, taking out private student loans, and financing cars and boats are all made easier with a high credit score. They're also easy ways to virtually assure that you will never accumulate wealth.
Please: don't look at having a high credit score as some sort of contest or sign of financial prudence. You can be rich with a low credit score and broke with a high credit score. There are times when it's important to have a good credit score (when you're looking to buy a house) and a history of responsible use of credit will make it possible.
Focus on doing things that will make you rich -- not carrying a balance on credit cards, making all mortgage payments on time, etc. -- and your credit score will follow.