CardHub.com offers recommendations of using your credit card overseas.
First, it is less expensive if you use your credit card for currency conversions when making payments in the native currency. Visa and Mastercard have exchange rates more than 8% lower than those offered by the average major bank.
Get a "no foreign transaction fee" card to avoid fees ranging 2-4% from foreign merchants.
Use a low-fee debit card when traveling because not every place accepts credit. It will also have low fees for withdrawals.
Also, when paying, only sign receipts calculated in the local currency. Foreign merchants sometimes offer to convert prices into U.S. dollars in order to charge a high conversion rate.
Lastly, CardHub.com suggests telling card issuers you will be traveling overseas. Some credit card companies may suspend your account if unusual transactions suddenly occur.