The MKIII headlight systems have built in rotation elements. Simply removing the small screw in the bulb shroud will allow you to rotate the shroud to your desired position. Then re-install your screw to solidify its position. There is no 'correct' position, it is based on your needs and preferences.
This allows you to adjust the light cast pattern, or beam, to your desired preference and to reduce potential glare to oncoming traffic.
You also need to pay special attention to the OEM beam adjustment screw located on your truck's headlight assembly.