Video tutorial on how to add extra light in to your photos using Photoshop. See it here.
DIY Ring Flash
Highlighting and contouring in Photoshop: Fill a blank layer with 50% grey and place it on the soft light blend mode. Then paint with either a low opacity (10-15%) white paintbrush to highlight or a low opacity (10-15%) black paintbrush to darken.
At the beginning of my journey as a photographer, I watched a lot of tutorials and read plenty of articles saying DO NOT TOUCH THE CLARITY SLIDER.