Imagine a light coming from someplace on the edge of the picture.. (even make a little lightbulb temporarily to use as a ref) then put the lightest parts on the side where that light hits this..and shade down to darker all the way to the other side (then get rid of the lil light bulb)..do this on a new layer so that if you don't like it, you can delete that layer and do it over... I bet you will like it better
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