Let's start with lighting. Using the iPad or phone display with a white screen as a light source works excellent on portraits. Pages in iOS or other word processor have a white screen background. Try putting the camera right in front of the face and the iPad at a 45° degree angle to make interesting shadows on the face. The 45° degree angle to the face has several advantages. It doesn't blind the person, it makes a face look less flat than light from behind the camera, and it doesn't make the nose look big. You don't want a long nose shadow on the cheek in most portraits.
For other effects you can change the color of the iPad screen (draw a colored square in Pages). Try blue to get a cold midnight look, orange or red for sunset, etc. Experiment with light positions. If you go for blue moonlight, the light might come from above. Sunset is shoulder level.
Try different portrait angles too. Turn the head 45° away from the camera and the body another 30 degrees away from the head, but still look into the camera. In addition to making portraits more interesting, angeling the head from the body can straighten out and hide double chins and wrinkles. If you take 3/4 or full length portraits, you can angle the lower body away from the upper body if you want to make the person look slimmer. This will stretch the stomach and flatten it a bit.
Most people have a “better” side of their face, but not everyone realize it. Ears and eyes can be different sizes. If one eye is bigger or more open, you may want to angle the face to have that eye further away from the camera so they look more evenly sized. Or if an ear is bigger, the smaller ear side may be best faced to the camera, and vice versa.
When you frame a person with the camera, don't let the photo edges cross joints like elbows, wrists, hips or knees. That will look weird. Let it cross in the middle of upper legs, lower legs, upper arms (if they are hanging along the sides), lower arms or middle of the stomach. Hands fully tucked down in pockets often looks chopped-off. Leave a thumb out of the pocket or put only the thumb in the pocket, whichever looks best. For the same reason, don't hide hands behind the back or head.
Avoid the subject letting palms or back of hands face the camera. Since hands are roughly the size of a face, they will compete with the face for attention. You don't want that, so put the sides of hands (the profile of the hands) towards the camera. Feet usually look better put at an angle away from the camera. In profile they might look big, and pointing directly towards the camera they can look like stumps.
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