Hi Dienle. Lovely piece of work, first of all. The effect you are looking for is called Chiaroscuro, which is a word coined by the Rennaisance Italians to describe light and dark, even ranging in one artwork from the lightest possible shade (white) to the darkest (black).
I see you have probably used a fairly hard pencil here, perhaps a HB or B. Maybe you can get more contrast in the darkest areas using a 3B or 4B quite liberally.
Chiaroscuro, interesting, I would have a search up the term
Yes, I was also thinking of using other types of pencils, although that would meant having to search out for it because art/stationary shops are scant in my area.
I see you have probably used a fairly hard pencil here, perhaps a HB or B. Maybe you can get more contrast in the darkest areas using a 3B or 4B quite liberally.
Just a thought. It's still a great piece though.