don't close your credit cards if you have 0 balance on them
Just take them out of your wallet and keep them in your desk or something. if you cancel them it'll actually lower your score by a few points. just dont use them at all or keep your use under 50% credit line and you'll be golden. Available unused credit lines look very good to creditors.
If you're applying for a mortgage or a carloan, the creditor does not go by your score alone. The length of your credit history as well as what your largest credit lines have been so far and how well you were able to perform goes into consideration along with your income/debt ratios.
Bottom line for handling CCs:
1) try not to open/apply for too many (you'll have a lot of enquiries on your report)
2) use the ones with the lowest interest but try your best to keep under 50% of credit line
3) don't close any 0 balance cards