The flash is one of the most important things in portrait photography settings. First you can use a little fill flash to improve your portrait, so when your camera exposes the background, your flash will light up your subject. While using the flash in the sunlight, it can sometimes make some problems of shadows across the faces and may burn out highlights. And for sure, you have to use the flash in the low light, especially when you photograph outdoors at night.
7. Shutter speed settings
You have to make sure that your shutter speed is more than your effective focal lens, like if you use 400mm of the focal lens, you should use 1/500 sec shutter speed or faster, You could use a little bit slower shutter speed when using a wide-angle lens, like 1/20 sec for an 18mm focal lens.
8. Fill the frame
You may zoom on the face, eye or mouth, so you could fill your portrait by filling the frame, which will make good details appear better.