As a professional photographer, it is my job to avoid making folks look ugly in pictures.
To do this:
Use soft lighting and avoid using an on-camer flash.
The natural light from a window is idea.
Set your camera lens to around 100 mm (or zoom your lens so the persons head and shoulders fill the picture when you are around 6 or 8 feet away).
Make sure your 'model' is ready, before you take the picture.
Get them to stand 3/4 on to the camera, and not straight on, or your picture will look like a police mug-shot or passport photo.
If all the above ideas fail, it miht be that your model has an uneven face.
They will be used to seeing themselves in a mirror, and when you show them a photo, they hate what they see; because it doesn'tm look like them.
Try printing the pricture in reverse, or showing it to your model reflected in a mirror.
I but they like the picture better when it is reversed.