Basic structures are well laid.
Your lines appear to be placed confidently and with intention.
The dark texture in the hair of the last photo suggests that you allowed your eye to catch on that specific trait and lost time to a single section. Subsequently the glasses and facial hair previously suggests the same. Instead, try to train your eye and think about the subject as whole, needing to be built layer by layer like a house, not piece by piece like a puzzle. Think construction not printing, sculpting with the pencil not drawing. Your base structures are already a great foundation to build on top of in this manner. Proportions are fine, lines have movement, a few are a bit flat but mostly your marks are lively.
Its perfectly acceptable to hone in on a specific section that you find interesting and want to really explore, but consider doing so logically in regards to the construction of the subject. If the hair is the focus then hang the hair on the head’s construction (frame) and leave the face a blank mask. Our eye doesn’t need the distraction from your focal point (the hair) anyhow, and neither do you need worry as your gaze flits back and forth peripherally between the hair and unfinished facial features, it’ll likely slow you down.
Concerning the hair instead of tracing line by line the direction of the strands try making an abstract outline using values (shading) as the mid tones, then make the brightest highlights apparent, and finish by blocking in the darkest shadows as you shade. You will already have the general suggestion of the hair quick and easy. Furthermore you’ll be free to make decided and sparing marks to accentuate the most meaningful aspects of the strands or texture with further mark making without the time spent filling in the body of the hair strand by strand. Instead of wirery the hair will have a greater suggestion of movement with the few marks you do make on top of these values as opposed to the many lines which subtlety conflict eachothers movement compositionally and confuses the eye as we can’t look at that many things at once.