The focus is the main thing in portrait photography settings and there are two ways of focusing, the focus and the de-focus, Focus is to focus the person himself so you could make the portrait more obvious on the person, so he/she could be under seen well. Nevertheless, sometimes maybe a subject is better to be focused in the portrait, when it is being more important, which you could focus on the subject of a watch or shoes, and make the person stand a few feet away. You can also, make the AF (auto focus) focus on the eye or the head. For this you will position your subject off center.
Change the ISO to make a sharp photo, and to avoid mistakes, such as a person blinking or without his perfect smile. You can change your ISO100 to ISO400 which will increase the shutter speed. But at night or indoors with low light, use ISO800, ISO1600, ISO3200.
5. Modest time
Try to choose your place and weather for your portrait, For instance, keep your subject warm because when he feels warm, he will give you the best smile. But keeping the same subject in cold weather, you may find his nose red or his ears frostbitten with a forced smile.