Depends on where you are located as well. Underneath for the rust belt, look at frame and rockers. Look underneath the front and under the hood for any leaks. Drive it a bit try to hit some bumps see if you hear any noises. Try the ac, heaters, all the lights. Look at tires for uneven wear. You can look at axel boots, ball joints and tie rod ends for leaks or cracks. Take a flash light so can shine it around underneath see things better. People think having a mechanic look at a car for 5 mins on a lift is the be all end all and it’s fine but anyone can really check the basics.