Answer: -Absolutely DO NOT co-sign that auto loan. Never, never, never co-sign anything with someone you are not legally married to. Everything may be fine now, but what happens in a year or two if you break up? Want to improve your credit score? Forget about getting another credit card. You have more than enough already. You should pay off the balances on your existing credit cards. Your debt to available credit limit ratio should never be more than 30%. At that 50% mark, you are killing your score.Only charge what you can afford to pay in full at the end of the month. Paying in full will do so much more to raise your score than getting another credit card. -ANytime you open a new loan your score will dip down a bit until a pay history is established. If you have no mortgage or auto loans open right now, it will raise your score after about 3-5 payments are made. I can see it going up to about 750 given the information you gave us there.To really boost your score, pay down the balances on your cards below 30 percent of your limit.Between the installment loand, and getting them cards down just a wee little bit more, I can eaily see a 770 in 12 months.