Co-signing a loan
Never co-sign for a loan if you can help it. The lender may place a hard inquiry on your credit report, resulting in a credit score deduction. If the primary signer can’t pay the loan, payment responsibility will fall on you. The last thing you need is a loan delinquency on your credit report, which can stay on your credit report for years.
I paid off my credit cards and medical bills. Two months later my FICO was over 50 pts. higher.