Don’t approach vehicles that you cannot see into (cars with tinted windows, for example).
Have the driver roll the windows down...both front and rear. If they can’t, then call them out to you. You can order out all occupants without reason so long as there was cause to stop the vehicle in the first place (Pennsylvania v. Mimms).
If the driver refuses to roll down the windows, then refuses to come out, no matter how nice or calm they are, that should be a red flag to you! Call for additional units!