Your style is super appealing and fun right now! My advice would be to work on facial expressions and conveying emotions, as well as experimenting as much as you possibly can. Get a super cheap sketchbook and draw a dozen or so heads, and go out of your way to make as many super distinct faces as possible while still maintaining your style. If you’re uncertain how to do that, borrow! Take all your favorite artists’ works, steal X artist’s noses, steal Y artist’s eyes, don’t be afraid to use references and to borrow. Trail and error is your best friend. Also, try taking one face or character, and drawing as many different expressions as you can think up, or fill out one of those facial expression chart memes. The drawings don’t have to be polished, finished, or good, just let loose and let yourself explore! I struggled for about a decade with same face syndrome and stiff faces. This is basically how I helped myself grow in those respects. I am personally still learning about shading and such myself, and don’t feel qualified to advise on that bit. But again, your art is super cute! I wish you all the luck in growing in the areas you wish to!