hey there, just did a quick paintover of your drawing, hope you don't mind! my first critique is that you should focus on the separation of light and shadow more. in the paintover, i darkened whole left side of his face ( from our pov ). a bit exaggerated so you can see it better. in your drawing, the whole mouth area doesn't have a core shadow, so it looks very flat. his beard on the light side should also be slightly lighter than the shadow side. next are values, the bridge of the nose is brightest on the face. everything else is darker. yet youre using that brightest value every where on the face, making the face looks flat. in the paintover, i darkened the eyes, forehead,and cheeks ( though i might have overdone it but it still should be darker than the nose bridge, even just a little bit ) for the hair, i recommend watching proko's video on hair if you haven't seen it yet. in short, try to group hair strands into bigger shapes. don't draw every single strand, design your shapes. another video i recommend watching is Sinix's anatomy quick tips on hair. honestly, i dont think you even need to spend time on the whole background. maybe just part of it, instead, focus all of your energy on the details of the face. and by details, i don't mean every wrinkle and strands of hair, i mean accurate values, proportions, shapes, etc. ( fundamentals ). here's an example by JOHN FENEROV: https://www.instagram.com/p/CPL-qllnK_Z/ the paintover still needs a ton of work and has lots of flaws, but i hope it can give a direction on where to go next with your drawing. hope it helps!