https://www.skillshare.com/en/classes/Sculpting-the-lower-part-of-the-face-in-Blender-3D/1266204962

Studying each part of your mesh will be on of the best tools available to you when looking for improvement or just starting out. In this class we explore the major parts of the lower face , like the mouth , nose and chin. You'll start at the basic shapes and slowly form each part.

Blender we'll be used in this tutorial , but most of the principles could be applied on other 3D sculpting applications. However a basic understanding of the app that you are using is necessary. Other than that all you need is a mouse (a tablet would be a plus) .