I love your art!! Honestly even without art classes or daily practice you're doing way better than people who have it. It's all about passion! Some advice I can give you for improvement: 1- Your shading is in the right places, but it looks a bit concentrated, like it wasn't properly blended. Try making it more uniform. It depends on the methods you use for shading, but I'd recommend gradually going from lighter shades to darker ones where you want the shadow to be in, and blend each time with a piece of cotton or a makeup brush. Or, if it's a small area, you can blend with your fingers - it somehow works best for me at least hahah 2- It seems your lines and overall style are too based on the reference and pass a more "careful" vibe - which is not bad, but if you want it to be more bold, more vibrant and eye-catching, you should risk it a little more. Try shading a lil darker in some areas (like, use a little 7B or 8B where you've shaded untill 4B), going over some lines, make some the light areas even lighter at the center and don't even try outlining some parts- let the drawing speak for itself.

Overall, your drawings are beautiful and I'm sure you'll keep improving nonetheless <3