If credit bureaus have more than one address or and incorrect address they will think that you move around a lot, which in turn can lower your score. Don't use a post office box for your home address. This often signifies instability to credit-scoring companies. Reduce the number of open credit lines. Cancel cards you no longer use, even if you have paid off your balance in full.
Lenders view open accounts, even with zero balance, as potential unpaid debts.
Do not apply for credit at a lot of different places. This lowers your score each time an inquiry is made on your credit status. If you are rejected, challenge the score and ask to talk with someone about the report. Be reasonable and interested in clearing the problem, not angry or outraged. Plus, their system allows you to guard against credit fraud.