The keys of the portrait
I've noticed, that the most important part of the portrait is ( you would've never guessed it..)the eyes. Every portrait I see first I need to carefully look how the eyes are shown. I guess in my work eyes will also be the key... But there is something also about the hands...

The colouring
There are lots of questions what to do with the overall colouring.. :/ Now I think it would be a great idea to chose 3-4 color complex and one more colour which would stand out. I think that would help to create a special mood of the portrait...