hey! first off, i couldn't do this kind of thing... i'm no 3d artist. but i can give you the anatomical side of it the way i would treat a drawing!
first, you should understand that to duplicate the human form is rediculously difficult... you see people evry day, so, you can't really fudge something withought having it get noticed.
another thing, if you DO want to duplicate the human form, i would suggest checking out any good anatomy for artist books... you should try and understand what's underneath the skin, so that you can convincingly lay down the skin on top of the exisiting skeleton... like your knees... you have a bone there, the patella, which is pretty prominent on anyone.. but you forgot to include it all together!
as for the neck, put 2 fingers in your own "pit of the neck".. there's a hole there

where the 2 clavicles connect to your sternum.
another thing, is remember the rib cage, and the pelvis. 2 huge bone collections that everyone has... describe these masses, and it'll look 10 times more human
i hope this isnt too much... i could go on and on... ( i love anatomy study)
you were pretty close on your latissimus dorsi though!:D
geese i love these happy face icons !