head is still entirely too small for the body. using refs? could you post them so we see what you're following/aspiring to?
the last pair of ribs meets the sternum just below the center of the chest. the rib lines you've drawn, and the upside down u shape that looks like it indicates the bottom of the ribcage, is just above his belly button. Keep the skeletal structure in mind. in fact, a skeleton should ideally be one of your references.
there's no definition in the arms. know where the deltoids, biceps, triceps, etc are so you'll know what to shade.
neck doesn't make much sense. learn the muscles of the neck. deltoids meet the trapezius, trapezius travlels upwards (primarily up the back), and meets the muscles of the "neck" themselves. the dip in the center of the neck is the point between the clavicles (collar bones). as such, it's high- it should sit lower than the top of the shoulders, with the clavicles running along to sit atop the shoulders.
reference, reference, reference
then check the how the separate parts of the anatomy relate to one another in regards to size and distance
repeat