Amazing job,khoatudiep. Amazing job on your class mode sketches!
Well, if I would, and could, provide you some commentary, it would be this: I love the animator's line you've put into those quick doodles, but I really need and want to see more of it. Why don't you please loosen and free yourself up, by doing 30 minutes of 29 second attitude drawings???? (1800/29=62 manner sketches)
The reason why you could do this warm up is because, it would, could, and should make your drawings less bland and stiff, and most cartoony, lively, and animated, in terms of your forces. My hat's off to you, and I hope you've found this completely and totally intuitive and productive.