How do I improve my drawings?

How do I improve my drawings? I am learning by myself with no teacher. In the past, I found this website, and I found it useful! But my drawings, which follow the tutorial, look a bit strange. Maybe I could modify something to make them smoother?

https://imgur.com/a/SC8Tk7i

These are actually really good drawings, if not traced. You didnt post a link to the tutorial so i cannot compare but i do think you could focus on drawing more feet, hands and faces as those seem to look a bit off in the drawings. Continuing to practice and really looking at the differences between your drawing and your reference will help you find the small details/mistakes you missed.
I really like the shading you did on some of the figures, it really brings out their volume.

Thank you very much. The tutorial is the book Force by Michael D. Mattesi. When I draw the head and hands, the photo is too small. It's true that I didn't pay attention to those difficult parts

it would help to have a bigger reference and take your time with your drawings. before you put in any details, measure out your drawing and try and follow a structural method. This helps increase the accuracy of your drawing if this is what you're looking for. You're doing a good job though, your drawings are all very good!

Thank you for the encouragement and advice! I’ll definitely try to use a bigger reference and focus more on structure first. It’s something I’ve been wanting to work on, so your tips are perfect timing. I really appreciate your support

I can't really help you :,)
I did try to critique your work, but really, its perfect. The most I'm doing is nitpicking.
Also there was this one posture I really can't figure out without the reference photo you used.

Anyways, yeah. Just keep up the good work!

Critique:
https://imgur.com/a/j13hPiz

Thank you，Yenaonorbit.   I’ve learned something: anything that is done half-heartedly will have to be redone from scratch… Self-learning, however, makes it easy to be careless with oneself…

These are amazing! Great work. This are overall great studies

Some of the things that i see that you can improve tough, its exaggerating the line of action a little bit further in some poses so it dosent look so stiff, for example in action poses like the second image, the boxer, i feel like you can push a little further the pose by making him lean a little bit more further, making the leg in the air a little bit more extended,and the arm more stretched, just to give it more power to the pose. small things like that.
 i also see some issues with some sizes of the head like in the second image, they are pretty big heads,except the boxer.

The last study on the last image is really great, you did the shadows and contrast very good and i see no mistakes. really great stuff and kep it up!