Car

Make sure battery has a full charge and connections all good. If the battery is down, can't do any testing. Use a battery charger. If it cranks good but won't start, have a helper crank it, while you check for spark at the plugs. Use a gage and check proper fuel pressure and check for fuel injector pulse. Check for applicable trouble codes? Those are the basic checks, in my opinion. To check for codes, at the least, you need an obd2 code reader that will work with your vehicle and read manufacturer specific codes as well as po codes.