One of the most fascinating thing about drawing is that it doesn't matter the technique or process you use. You will still arrive of the same goal.
What really matters is understanding where there is light and shade. Understanding where there is high tone, mid tone and high light will help you get your job done.
Here I used scribbles to shade and add tones to the work.
At first it looked freaky while I was working
But gradually I built my forms with doodles adding meanings to the work.
And this the final result.