Every trader should have at least one but no more than 3 credit cards. If you have more than 3 cards, it is suggested that you cancel them. If you currently have outstanding balances on your credit cards, it is suggested that you transfer them to cards with lower interest rates and do not start trading until you have the balances paid off. It is unlikely that your trading returns will exceed the interest rates charged on your credit cards during the first couple of years of trading.
Credit card balances should be paid in full and on time every month, thus making them more like a debit card but you get the float of the money (i.e. the time between making the purchase and paying the credit card bill). In the rare occurrence that you cannot pay the bill in full, you should absolutely pay the minimum balance and then pay the balance in full the next month. If you cannot pay the balance in full by the next month, you should stop using the credit card and only use a debit card or cash for necessary purchases. Using the credit card should be a matter of convenience (not having to carry cash). Credit cards should not be used to make purchase of things that you cannot afford or things that you don't absolutely need. A flat screen TV would be an example of an item that a trader might not be able to afford and does not absolutely need.