Good credit is established by not so much of the amount you are in debit but by the length of the indebtedness to a creditor and how many late
payments you have accumulated from the very start of the loan.
Get a $1000.00 Visa or something similar, maybe even two and make sure you pay the minimum amount every month.
Every time you are late on a payment that knocks you down a few points on your score.
Have numerous debts that are listed upon you and make the occasional late payment on any of them and it becomes difficult to regain your total score.
Anther way they calculate your score is how much of the available credit do you use on a given card or line of credit, this is something that I just recently
learned myself.
They say to keep your score high one should only use less than half of the available credit given to you.