Depends on how old the car is. First thing upon returning from buying a used car is to give it fresh oil and filter. Obviously check when it was last serviced when looking at it, and even if it's had a recent service, I always give it a proper inspection. Ie; plugs out to check them, air filter out and replace/clean as required, new oil and filter as said, and get it on the ramps to go over everything I couldn't on initial inspection.
