With photography you should always be learning something new about your gear; I did yesterday. This tip works with Canon (sorry, don’t have any Nikon gear).
When in LiveView (enter pressing the Start/Stop while photo is selected). You can then use the magnify to zoom in an focus on the point you want. For portraits, it’s the eyes. Hope this tip helps you as you grow in your skills as a photog.
Examples are the Canon 6D and 5DmkIII.