Just do normal checklist as any car you buy. If you see any problems, take photos and go inside to get those documented by Tesla too. Basically check and try everything you can on spot. If you notice anything weird or broken, you can still make a complain afterward.
Check all the exterior (outside) very carefully, because any misaligment or scratch in the paint job is hard to prove afterward. Check the bottom of the car too. Try open and close frunk and trunk.
In interior try all basic functions: screen, seats and belts, etc. Check that you have all charging cables included (Type 2 cable and mobile charger for normal plug). Open glove compartment and check if there is USB drive.
If you need to know what to check. Just type "Model 3 delivery checklist" on YouTube. You will find a lot of there videos.