The main thing that stands out to me is the outlines. This is something I really struggle with too. I tend to make my initial outline too dark and the images gets confused due to tension between my tendency to outline versus building up the volumes with light and shadow. The image on the left does a great job of this but the one on the right seems unsure whether to define the shapes with outlines or with areas of dark and light. For instance his left ear. You can push the value of the hair behind the ear, in fact the whole lef side of his hair, much darker and get rid of the lines. A light outline on the highlight side of the features makes sense if you are keeping the background white instead of filling it in. I think you can darken the value on his neck, under his chin (image on the left again) but be sure to keep the reflective highlight along the jawline even in the shadow area. This will really make the image convincing and increase the feel of volume. If you wanted, I think you could also fade the outer edge of his hair towards the back of his head so there is no crisp edge. This would add a nice depth.

ma'am this is amazing , just a few pointers . I think think the separations of the light and the shadow area should be more recognisable (the core shadow ) and lastly the local value of the hair and the lips are always darker than the skin tone . rest it looks great :).

These are really awesome! Not sure how true to the reference you were intending to go, but if you were then the bridge of the nose shapes need to be straightened out a bit. I think in the second one, the additional shape adds, but in the first drawing, the lack of structure makes the nose a bit wavey

Hi! They are both great studies! About the first one. I think you can push more the shadow mass on the right. The eye socket should be darker than the cheek. Also, I think you accentuated too much the angles of the face on the right (see attached) and on the nose.