I recently read an article on get rich slowly - www.getrichslowly.org - where the author suggested abandoning using credit cards and using cash instead. I thought this was an interesting suggestion, although one I might find it inconvenient to implement in practice, but I do agree that it is best to simplify one's credit card situation as much as possible. My thoughts on using credit cards are as follows:
1) Credit cards are a terrible way to borrow money; the interest rates are huge compared to any other type of loan.
2) Credit cards can be a useful way to pay for many purchases, but only if you already have the money for them.
3) It is worthwhile signing up for a credit card with reward points or airmiles. (Mine gives 2% cashback.) These benefits are only worthwhile if you pay off the full balance every month, however, as they would not come close to offsetting the interest payable.
4) Having used various cards in the past, I have now simplified my situation to the following; using one Mastercard for all household bills and most large items.
5) I have online billing, meaning a) you can check the state of your account at any point, and b) it is set up to pay the full balance every month, so you don't need to bother with a bill and worry about avoiding late fees. If you do not have this option, make sure that you have a way of keeping track of the due date of payments, so that you avoid running up charges for late payment.
6) If you need to have a back-up card, for instance for travelling or to pay for large one off items, keep it tucked away somewhere safe, and not in your wallet, when not needed.