The chin is a golf ball.
Artists can get into a lot of trouble if we forget that the chin has structure. That it is round. We can be in a big hurry to labor over the more popular features- the eyes, for instance. (If we were comparing the features of the head to kids in high school the eyes would be the blonde, popular cheerleader.)
Touch your chin. Golf ball.
Tip- put your models in natural light from a window or at least in one light source from a floodlight. Do not use a flash. Do not paint a portrait from a school photo. (Do not pass Go, Do not Collect $200) The lighting is too flat. There are too many lighting sources. Just becasue a photo looks cute does not mean it will work as a reference for a painting. You need structure. You need to see a round chin. Use one light source and find that golf ball.