If you get denied for a major credit card, try applying for a retail store credit card. They have a reputation for approving applicants with bad or limited credit history. Still no luck? Consider getting a secured credit card which requires you to make a security deposit to get a credit limit. In some ways, a secured credit card is more useful than a retail credit card because it can be used in more places. Certain subprime credit cards are geared toward helping customers who wish to rebuild their credit; however, make sure you choose legitimate offers and compare the fees and interest rates before applying.
Credit scoring models usually take into account how much you owe compared to how much credit you have available, called your credit utilization rate or your balance-to-limit ratio. Basically it's the sum of all of your revolving debt (such as your credit card balances) divided by the total credit that is available to you (or the total of all your credit limits).