Well, for three weeks it's definitely great. Just keep practicing more and more, at this rate you should be good even in just a year, but who knows how you'll grow from this point. You just really have to study bodies a lot.
What I recommend for proportions is just literally googling it and checking. You should know simple things, like hands. The hands you draw are way too small. Mostly what you have to do is pay attention.
Okay, here's what I want you to do: find pictures by manga artists you like, and copy the whole picture. And actually pay attention. Really pay attention to every detail. Notice how he draws mouths. How he draws eyes. How he draws eyes. How he draws things from this angle, how he draws things from that angle. You can pay attention and learn this just by looking, but actually copying it for yourself is very helpful. It's important. It's great training for your eyes. When you copy his character, look at the arm and think, "okay, how big is the arm compared to the body?" or "where does his stomach end and legs start?" Usually manga characters are divided into heads, like
this picture, and usually the chest/stomach is two heads, and the rest of the heads are crotch/legs/feet/whatever. But I can't type out every single thing, like fingers should be this long, hands this long, etc. Some of it you will either have to google for yourself, or to learn by observing. I think learning by observing and copying is the best, it's the most dynamic, and most involved. Try even copying whole pages. There was a while I copied a full chapter from Bleach, down to inking and screentones. I learned a whole fucking lot about how to draw action, and also things I didn't even think about -- like the precise way Kubo draws mouths and noses and eyes, things I didn't even notice before.
Now next thing, if you want to actually draw manga one day, you will need to learn how to use a nib pen with ink. Get a g-pen. If you don't know what a g-pen is, then read Bakuman. Reading Bakuman is the first thing you should do if you want to draw real manga, it will motivate you and teach you a lot of things. But anyway, yeah, nib pens and ink are a priority. The earlier you start, the better.
so those are my tips for you:
1. In order to learn and understand proportions, look up and read tutorials, and also copy lots and lots of pictures by your favorite artists. Notice
everything. Understand why they draw things the way they draw them. Really think while you're copying.
2. Learn about proper manga tools like nib pens and ink. Get some for yourself.
3. Practice. A lot. You have a long long long way to go.
