Everybody knows that one the easiest way to ruin your credit is failing to pay your bills in time. Fewer people know that keeping a high credit utilization ratio (over utilizing your credit line) makes a hidden but serious negative impact on your credit score.
Credit score building basics - start with a credit card and an credit building installment loan, pay every month several days before the deadline, keep your credit utilization very low (use no more that 7-10% of your credit limit withing a billing cycle). If you follow this basic but strict rules, you will be surprised how quickly your credit can return on good or even excellent territory