Ask for a vehicle history report to tell if its been wrecked before. Mechanically wise, if its higher miles ask if the timing belts been changed and if they have proof. Any older higher mileage vehicle will have 2 main issues that can completely ruin it. That's if the timing belt snaps or if the headgasket blows, those things are major repairs. If its stick shift then ask about the clutch. Best to have it looked over by a mechanic before buying.
Private seller or dealership? Ask for maintenance and accident history or get the VIN and buy the Carfax report yourself. Check mileage, check for rust and damage. Make sure all gauges work properly. Listen to it run and take it for a test drive. Check under the hood, but if you don't know what to look for bring someone with you. You'll find the strangest things sometimes.
Best thing my grandpa taught me is have them change the oil in front of you and have the mechanic run a magnet through it. If there is weird gunk on the magnet run. Also do a visual inspection on engine for leaks and rust
A test drive can tell you a lot about a car...take it for a spin ALONE if the dealer will allow...if someone rides with you they will talk and distract you. Listen for unusual noises and get a feel for the car. If it is a used car ask to see service reports or receipts and ask for a carfax report to prove it has not been wrecked. If you know a mechanic you trust take it to him and have him look it over or drive it. Good luck and happy motoring...
good tires, fluids (oil, differential, etc) recently changed, cleaned spiffy inside and out, any damage (from wrecks, hail, etc), make sure nothing grinds or skips when you drive it. all the switches work