Ask the current owner about any collisions or other types of damage the vehicle has sustained.
Make sure you know if the odometer had ever been rolled back and if the vehicle has ever been involved in a flood or natural disaster that might have a lasting effect on the mechanical part of the car.
Take notes of mileage, features, likes and dislikes and price.
Take a magnet it can identify any corroded spots hidden underneath a good repair job.
Take a flashlight it allows a clearer view of hard-to-see enging and undercarriage parts and makes finding leaks a little easier.
paper towels are good to have on hand to check the engine fluids.
Look at the car from all four sides, the top the bottom, and from any other angle.
Always look at the upholstery and trim of a vehicle.
make sure everything works, try the turn signals, windshield wipers, air conditioning, heating system, music, locks, and windows.