[Kiel]

1) multiple credit lines help your credit, and diversity of credit type (student loan, personal loan, car loan, credit cards) helps your credit score
2) length of credit history (how old your oldest OPEN card is) is a major factor - even if you pay a card balance down to 0, DO NOT CLOSE THE ACCOUNT YOU WILL HURT YOUR CREDIT
3) pay ON TIME EVERY MONTH or you might as well punch yourself in the face
4) the ideal balance/credit limit ratio (known as "utilization") is 3-8% - basically meaning if you have a $1000 credit limit, the ideal balance to maintain is 30-80 dollars. yes it's difficult to maintain and NO you should not freak out if you can't meet that. but DO NOT MAX OUT YOUR CARDS, YOU WILL HURT YOUR CREDIT SCORE
5) the best thing to do with a credit card is keep it active with a low balance. buy coffee every day? put it on your credit card and PAY THE BILL OFF at the end of the month.