In terms of lighting, you should up your contrast and use more darker darks against brighter brights. Experiment and be more risky, use both ends of the light spectrum. White against black shines far more than light gray against dark gray. Especially for the necklace. I would've never noticed that it was there if you haven't mentioned it, especially since its nearly the same color as the skin. Metal should reflect more light and shine brightly.
Your brush strokes need more variation and needs to taper off. Are you using a pen or a mouse? It doesn't look good when you can see the circular shape of the brush, especially in places like the eyebrows or where the highlights are (it's most prominent on his right pect/chest). If you're using a pen, set it to vary in width. If you're using a mouse, try not to think of highlights and shadings as making lines, try to think of it as filling in a space with color. These spaces should taper off to a point instead of being round.
View attachment 121036
That right pect and the chesthair area is also problematic since it doesn't transition well. From your profile pic, it almost looks like it got cut off or something. The problem is that shoulder highlight ends where the chest highlight begins, which is also the same level where all the chest hair ends, which is why it looks like the image got cut off at that line. I'd suggest making that transition more varied so they're not all at the same level. Make the shoulder highlight go lower or the chest highlight higher. Make the chest hair end in more of a curve instead of a line.
Chesthair also looks messy, I suggest making them more uniform and aligned, flowing in the same direction instead of pointing in random ones. Having them follow the curves of the chest to accentuate its shape would be a bonus as well (Notice in MonMarty's image, the chesthair flows together in a radiating direction).