Protecting Credit Cards
Credit and debit cards are very similar other than that credit cards are protected by a federal law that limits your liability for unauthorized transactions. Therefore, it's generally best to use credit cards given a choice because you won't be liable for unauthorized charges (and have a variety of other protections as well. Still, it's not fun to have to replace a credit card so here are some tips to keep them out of the hands of bad guys:
Watch for skimmers
It's not incredibly likely that restaurant servers or other store employees will use a handheld card skimmer, but if you're worried, you can ask to pay at the register. Much more likely is to find a card skimmer "in the wild"; usually attached to a credit card system of a gas pump. Always look for loose or mismatched pieces where the cards would be inserted. Go ahead and give it a firm tub and shake just to see if something comes loose (and if one does, call the police).
Cross out your card number on receipts
This shouldn't be a problem anymore, but I still find stores now and then that have really old credit systems where it's a good idea to make sure the full credit card number isn't visible on the receipt. If it is, scratch it out and if the store/restaurant employee complains, just remind them that printing the credit card number on a merchant copy is against federal law:
Don't let online companies store your card
It's simply a matter of odds. The more places your card is stored online, the more likely it will be caught up in a breach. If you don't shop somewhere often, decline to store payment information.
Use Virtual Cards
If your bank has this feature and you wish to make a purchase with a store you don't know or trust yet, use virtual credit cards. These are one-time use numbers attached to your real credit card, but using a number that's only good under certain restrictions (like a limited number of transactions, specific time span, one-time use at only one store, etc.).
Avoid contactless pay systems
The last thing you should have to worry about is your credit card being accessed remotely without your knowledge, but the wireless chips used in some cards make that possible. For example, the EZ-Pass system uses an RFID chip that can be read and easily copied from hundreds of feet away. Once copied, someone can go through the tolls while leaving you with the bill. If a system doesn't require any physical contact, just proximity, then you're probably using RFID and you're at risk (this is not the same as chip cards that still require actual mechanical contact and can't be waved over a reader to pay.