5 min sketch. First practice

Great job on your first practice! Keep on drawing, as you'll improve pretty quickly as you stick with it! I really like how the pose is very readable and the viewer can easily identify squash and stretch in the drawing.
I think you should improve on the anatomy and perspective. Those are very wide ranges of critique, so more specifically, I think you should meausure using your pencil more frequently. This video explains measuring in detail: https://www.youtube.com/shorts/sdnvjyVOP4k
The video talks a lot about long poses, yet simply lifting up your pencil to check relationships and angles is infinitly helpful with short poses (as well as long ones!)
Your grasp of anatomy and perspective will improve as you continue drawing, so keep practicing!

First of all great job for first practice!

The only main thing for improvement I can see is the left leg (the one sticking out). I would try to keep looking at the picture as a whole instead of focussing on one part of the figure as you're drawing. This is difficult to do but results in a clear view of the effect of what you're currently drawing on the entire composition.

Lastly as a small tip. I would go a little lighter on the drawing. This will make it more easy to make changes and to add details later on.

You will see the fastest progress by just practicing. Just keep drawing. Frequency is always more important than quality when practicing!