If you filed bankruptcy under chapter 7 you will be able to obtain a new credit card very shortly after filing. Most banks will want your business, because (1) you have reduced your debt, (2) cannot get another bankruptcy discharge for 8 years, and (3) the bank will be able to charge you a high interest rate.
Most individuals are able to get unsecured credit cards, however, in some cases the bank my require you to get a secured credit card. A secured credit card is much like the traditional unsecured card, however you will be required to secure the card with a deposit. This is different than a prepaid card. With the secured card you will still need to pay the monthly bill.
If you are in chapter 11 or 13 you are not permitted to get a credit card or other loans until after the case is over.
In either chapter getting a new card and using it responsibly will increase your credit score and rehabilitate your credit score. Using your card responsibly should include paying your bill on time and never charging more than 30% of your credit limit.