And I have to admit ... wow! This is really a great start for your sketchbook journey! I love your lighting, the details and your rendering skills and even more so how expressive and vivid the emotions in your illustrations are. Especially in the portrait pieces!
A small thing I'd recommend to you is probably flip the images a few times while drawing to correct small shifts in the facial and body proportions. (Or use guidelines to measure the proportions) Sometimes they are very slightly off. But that's really just nitpicking! Overall your work looks great already so... I am looking forward to see more of it and how your journey continues! :)