Always set your intention before you start a piece. "I want to make the viewer feel...." "I want to paint a bust composition that is..." Etc.
Trying to do one of these quick paint overs a day when browsing in the morning. So here goes.
You can group and simplify your values a bit more. I used two tones on the face that you had there. That was it. Plus the rim light of the spell.
The structure of the head has planes and forms just like any other 3-d structure and you can paint based on that. Find 'Reilly Method" Head or loomis Head drawings for example of planes of the face.
I pushed his hair back a bit with the color of the background on the right.
Focal point is the face so obviously we want to spend our time there.
I added light on the hand because that light of the spell will cast light but I didn't spend any time on the hand.
Take all critiques with a grain of salt and more information will always help the 'critique-ers'
Hopefully that helps and can get you started.
Cheers.
