Looking at your referenced copies, I think you have a really good eye for proportion! and this will definitely help you in your studies.
Subeta's base hair colour is pretty much my favourite haircolour of all time. It's my go to colour that I eventually switch out for others a lot, but I just love it so much heh
On your persona drawing: The one without the staff/spear is very open, welcoming and balanced (character wise, though I don't feel it was particularly unbalanced as a composition. Straightforward isn't always bad)
The staff is rather close to the face, held very high up and a pretty strong angle/diagonal. Now, I'm not sure what your goal is expression wise. What do you want this piece to tell the viewer? (please share ^^ )
Now the staff looks like it could drag over the floor and that its potentially in the way rather than an aid. The wing positions also add a little bit of an air of instability. I'm not saying they should be symmetrical though (perhaps consider folding one a little (or a lot) ) or go for contrast, it really depends on what you want with the piece!
Birthday drawing: Atmospheric pieces with high value contrast bring it! Of course you're still sketching and getting a feel for this piece but I do like it already.
Some pointers that you may already know or work on (or asked some feedback for) :
The hair is a bit boxy-shaped atm.
The mouthcap should follow the shape of the nose and then slope back towards the chin, if you want it to follow facial contours. There's now an extra slope, or maybe that's just his nose too?
Is his pelvis (mostly) pointed towards us and is he turning his chest and head towards the light? Is it a sudden movement or a more controlled one? I'm not sure about the gesture line. I think its important to get that clear first and draw the anatomy underneath the shirt, so you can figure out the placement of the ribcage, etc which will influence how the sternomastoid (most prominent neck muscle) will look along with the folds on the clothes.
The ripped shirt: I'm a bit unclear what parts are whole and which aren't. Remember that the ripped textile will hang and that volume most likely still exists but looser unless it was torn out of the shirt entirely. Focus on anatomy first, then the folds will come more naturally
You can try to push the background further back a little. The lone pipe placement will help determine the feeling of spaciousness so move it around to see what it does and how it could work for you.
A flashlight has a very distinct light shape and strong intensity that would also affect the space before it hits the character.
Here it is unclear from what angle and from how far away the flashlight is pointing (affecting the hardness of the edge of the light and its intensity) I'd establish that first so you can get a better idea of where to draw in the light/shading and its values.
Or you can decide it's moonlight (or other) coming from above which would likely make for a much softer light.
The shading of the room also needs to be consistent with whatever form(s) of light source you choose (but I personally find light placement tricky at times!) Trace back the rays of the light that you like to make sure they originate from the correct place.
Hope this helps a little Good luck! Looking forward to your WIPs!