What is the best thing to do with your income tax refund, i.e., the return of your enforced, interest-free “loan” to the U.S. Treasury?
If you have any credit card debt, pay off principal.
If you have no credit card debt, pay down some other debt, other than your mortgage.
If you have no debt to pay down, make a contribution to your IRA.
If you are maxed out on your IRA, set the money aside in a special bank account for your next car repair or new tires. This way, you can avoid charging this to your credit card. If you can get an extra year out of your car, you can defer purchasing a new car for another year. (Do this for the next five years. Then buy a used car.)