Hmmmm...well it depends on what I'm practicing for haha
but in general, I usually use my favorite characters as models for what I'm practicing. If I feel like practicing shading, I use a particular character whose face might be more angular and more fun to shade. If I want to practice gesture, I use the more cartoon shaped characters that I've created. If I want to practice expression, I use the characters that I feel have more flexible faces and designs.
Which brings me to my next point: just be in the moment of what you want to practice. If you want to do shading, do shading. If you want to do lighting, do lighting, etc. Do it when you feel the most enthusiastic about learning new things about your own style.
Also, it's good to look at tutorials and practice what you've learned from them, but it's also just as important to practice your style in itself to learn what you're most comfortable with and what you feel is the most compatible with your style. My older style did really call for traditional shading, I would just airbrush some light on one side and touch it up and et voila! I was done.
It's okay if you feel your style is a bit inconsistent because your style is always evolving and it's good to keep things changing!
Make sure that when you practice, you're actively trying to get better and you're not just doodling. SOME STRUGGLE IS GOOD
And I mean...practice...practice a LOT...like...10,000 (not exaggerating) hours of practice will make you good at anything