Public records such as a tax lien, mechanic's lien, foreclosures, and notices of default can drive your credit score down very quickly.

Sometimes, an unpaid medical or utility bill will be sent to a collection agency. Many people don't know this goes on their credit. This is another factor that brings credit scores down.

If you have credit cards, you should try to keep the balances below 50% of your credit limit. Having credit cards that are maxed out will significantly lower your credit score, even if you make your payments on time.

Whenever you make a large purchase - a new car, furniture, etc. - it will lower your score temporarily until you demonstrate you are making the new payments on time. For this reason it is important to not make any large purchases if you are thinking of buying a new home or refinancing your existing mortgage. Wait until the new mortgage has funded before making any other purchases.

Too many credit inquiries as a result of multiple credit applications within a short period of time can also lower one's credit score. Therefore, one should avoid applying for multiple credit cards simultaneously. However, getting your own credit report does not count as a credit inquiry and has no effect on the credit scores.