Maybe give this a try on the next one when you're adding shading.....light tonal value, medium tonal value, dark tonal value. Keep them distinct ( that will add dimension and emphasize the forms )and don't fall into the "smudging with your fingertip" trap ( that just makes one gray haze over your drawing ). Try looking at ANSEL ADAMS photos, he was a master of tonal values. Keep practicing, looks good.