Indoors, use a north-facing window on a bright day. This will give a soft illumination that flatters the subject. Get them to look into the window and shoot from the side for an attractive profile photo. If they turn to look at the camera, you will have a portrait lit from the side. Use a reflector on the side of the face opposite to the window to add details to any heavy shadows.
A reflector can be a sheet of white material or card, or even the page of a newspaper. If you don’t have a stand for the reflector, see if there is anyone available to hold it for you. If you are shooting just a head-and-shoulders view, it’s even possible for the subject to hold a reflector below their face, just out-of-sight of the camera. Reflected light from below gives a glow to the face.
A sheet can be hung behind the subject to hide any distracting elements in the room.
When shooting outdoors, keep the sun behind the subject. This puts the whole face in shadow, giving soft illumination. To avoid underexposure, increase exposure compensation by around +1.
Alternatively, activate the flash on the camera. Autoflash exposure will usually give good results without the need to make further settings.