David Bach, author of the Automatic Millionaire, wrote an article for Yahoo Finance entitled Nine Steps to a Great Credit Score. It's fairly basic stuff, but here's one bit of advice that I didn't know.
Ask lenders to report your credit limit.
Ask your banks and credit-card companies to list your credit limit if it's missing on any accounts on your credit report. If you don't, Fair Isaac may assume that those accounts are maxed out even if you haven't borrowed to the limit. This simple step could improve your score by as many as 50 points!