Most DSLR cameras are sold with a "kit" lens included. That's usually a zoom lens, almost always with a focal length of 18-55mm or 18-70mm. That can be a useful lens, but often our first impulse in how to put it to work results in disaster. Here's what I mean:
I ask one student to photograph another. Almost every single time, the student will stand up, point the camera at the other student and -- without thinking -- zoom out. That leaves them a few feet away from their subject using a focal length of 18mm. The resulting portrait isn't great.
Here's the thing: an 18mm focal length provides an "expanded" space. To see this, stand in a corner of a room and look with your eyes. Now look through your camera with the 18mm focal length and look at the space: you'll get the impression of a much deeper space. Zoom to a longer focal length and you'll feel as if the space is more compressed.
That "expanded" space is not flattering to the human face, generally: there can be an impression of a larger nose and larger chin, for example. The "compression" a longer focal length provides tends to create a more flattering image. Take a look at the next magazine rack you walk past: most of the faces you'll see there tend to be photographically compressed.
Try a further experiment: using the 18mm focal length, frame a person from just above their head to just about the second button on their shirt. Take the shot. Now, move yourself backward, change your focal length to 55mm (or 70mm) and get that same "two-button closeup" framing. Take the shot.
Compare the two and you'll see: focal length can have a transformative effect on a face. The same person may look quite different in these two shots. Usually, the longer focal length is perceived as making a significantly more flattering portrait.
Also, notice that most likely you'll now be throwing the background out of focus when using this longer focal length, depending on the distance between you, the subject and the background.
So consider forcing yourself to automatically zoom to telephoto when you decide to take a picture of a person. That 55mm or 70mm length can work just fine -- but you have to decide that's what will work best and, as always, force yourself to take control of the photograph you are making.