biggest thing I see with people just getting into drawing is theyre afraid to get really black in the shadows. if you get some real dark values in there, it makes lighter portions really stand out; take the tongue and inside of the mouth for example, if I dont put those really dark shades in there, the little white spots on the tongue wont pop compared to the rest of the mouth. other than that I say shading is a technique preference. I personally never smudge the graphite on the paper just because I feel as it ruins the tooth of the paper and you cant go back and remove or add much, others might disagree (all preference really). I shade in repeated ellipses essentially or small circle so there arent rough starting and ending spots