Do you have a reference that you're using for this pose? There's definitely some weirdness in the anatomy and the way the arms are moving, but if you have a pose you're working from it might help to see what you were going for!
I really should have used a reference for the general pose but i didn't in this case. I used one for the hands though but that's about it. I just sketched a pose on my sketchbook and attempted to transition it to digital.
What's the weirdness in the anatomy? Can you explain it to me?
Their grip on the bow is up way too high, should be slightly below center with the other hand pulling the string back in a way that the arrow would shoot over the hand holding the bow. Also you typically don't use your pinky when drawing back a bow string.
Their right shoulder/upper-arm is too far away from where their head is, because when you raise your arm that high the collar bone and shoulder muscle tend to come with it and fill in the gap there. And the forearm feels much longer than the upper-arm.
The left arm also seems like half the length of the right arm, and bowing (excuse the pun) in an odd way, like it's bending at the elbow but not in the right direction.
And the location of the left knee is kind of ambiguous since on the other leg the shorts end clearly above the knee but the leg in the back seems to bend somewhere in the thigh.
I think you could definitely benefit from trying to find reference photos or even doing the pose yourself and having someone take a picture.
Definitely seconded Kayke on getting some reference of some kind -- even if you can't find the exact pose, just looking up pictures of how archers hold bows will help you avoid basic errors like gripping the wrong part of the bow, and trying to make the pose yourself while looking in a mirror -- even if you can't get a photo -- will help you figure out what poses a human can be in naturally.
In this case, the position of the arm is literally impossible!
(forgive the pyjamas) your character's body is straight on, like the bottom photo -- but it's impossible for a normally jointed human to turn their shoulder straight up like that -- this is as high as mine will comfortably go!
If I want to get that arm pulled way up like in your sketch, I have to turn and lean my whole body over to point my arms in that direction, like in the top photo. Trying to have both poses in the same picture makes it look weirdly broken.
Just taking that into account, without looking up any specifics of how to shoot bows competently, you'd get something more like
I'm not sure about those legs, either -- it might be worthwhile to look up some photos of folks jumping back, if you can, or try to hit the pose you want yourself and see what works best.
Ultimately, all the digital colouring in the world won't help an image look better if the underlying construction isn't there -- if the anatomy is impossible and the clothes have to do impossible things then it'll be impossible to make that shading look right, no matter how you render it!
Everyones already said a lot on anatomy but one thing that I noticed is uneven arm length, and it can be tricky to figure out at first but heres a good trick i discovered a while back!
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so you got your basic character base
figure out where you want your hand to be, connect it with a line to the shoulder, then eye the middle of that line and draw another going out in the direction you want the elbow to be at
then you connect it all and adjust if you need to
Everyone has given some good feedback so far. Reference is definitely your friend! Don't be afraid to use it!
I also suggest trying the pose yourself, so you can see how it feels, and if it is even possible. I find it very helpful to act out a scene and pay attention to how I held my weight, how I twist, whether I was able to keep my balance, etc. That will help you create better more natural poses.
Oh I actually didn't know that about the bow. I'll make sure to do my research the next time I do something like this. It will probably be helpful.
Yeah the shoulder on that arm was more of an afterthought. Like I thought "oh I forgot to consider the shoulder" but I didn't bother to fix it. My bad.
And yes, I should definitely use a reference next time. In fact, I'll try to start this from scratch with better anatomy.
Thanks for the references! Also thank you for the pointers on how the arms helps move the torso. I didn't really consider how the torso moves along with the body (hence why I said anatomy is one of my many weaknesses in art).
So I guess this means I should consider how the entire body moves when you move one limb? Its probably something I should have considered but I never really did. Odd.
Yeah I'll have to look up some references for the legs. Now that I look at it again, I think the leg moving back looks particularly weird and off. I'll look for something similar.
You're right about the point on digital coloring, but I still think the shading is something I should work on. Or maybe use a brush to shade? I don't know.
Thanks for your help!
....And these are some decent leg references. Although, i wasn't trying to make him look like he was jumping, more like a standing pose; Though this might be a good reference to work from.
Hmm...now that I think about it...just from looking at the reference...it was probably a mistake to make his right leg be the one that moves forward. It would probably be awkward to move that way. Instead maybe the left leg could be one that's moving forward and the right leg could be moving back.
Now that I think about it, that would be a much better pose. Does anyone else think so?
Ah, thank you. I never thought about this approach. It'll probably help a bit with foreshortening too. I'll make sure to use this when I try to "fix" this artwork (and probably everything else I make from here on out)
Yeah, as I said before I really should not have neglected the use of a reference.
Posing myself is not something I do often. I probably should though, especially with the pros you just mentioned.
EDIT: I'll share the sketch with the fixes mentioned. This could be a good way to apply the new things I learned.
Here is a redo of the pose. Its clearly a sketch (since I'm only covering the pose for now) .
I feel a lot more satisfied with the pose compared to the other one. Though it has a few issues, I know the left arm is a really bad arm anatomically (I basically skipped the bottom portion of the arm by accident. But for the purposes of criticism I decided to leave it for now) and now that I look at it the right arm's anatomy is a bit off as well (I tried to use @stnmaren 's method. Which helped but the arm still looks off to me.)
But I think I got the basic pose right. It looks a bit better, probably more natural. Though that's just me, what do you guys think about it?
EDIT: Yeah will definitely redo the arms.
Unfortunately, stnmaren's method doesn't work for foreshortening. When you're dealing with bows, you encounter a lot of it.
I'm going to slap your wrist a little bit, and say you didn't look at the reference hard enough. 
Let's take a look together.
Archers always hold their dominate hand close to their face. Why? To get precise aim! With any two-handed ranged weapon you'll have one hand close to the face and the other parallel to balance the projectile's exit point, I think that's maybe why your arms feel stiff or wrong.
Also if you feel lost on the legs, find something similar and combine the pose! Never be shy about it. Eventually it'll be second nature. Feeling lost? Fire up the google images. Get results. I swear it works or I wouldn't keep nagging on about it. 
Oh okay. Thanks for explaining all of that to me. There's quite a bit I didn't really know about archery that I probably should have looked up.
I'll look for a leg reference that works best with the pose I want to make.
I guess I should try to make another sketch with all of this in mind (and with some references of course). Or maybe a number of sketches. I'll post the results a bit later.
Thanks for the advice, I think this helped me learn a lot.
I ended up making three poses.
This one I think probably has the worst torso. Not defined enough to me if that makes sense. Also the feet placement is clearly off to the point where they look like they are in the same plane perspective wise.
This one is better but now the hand is not even close to the face. Also the torso is a bit too long (I might have subconsciously tried to emulate @JessJackdaw 's style. It just looks off compared to the rest of the body to me.)
The feet placement is better, but its still off.
I think this one is the best sketch I have. It has issues though, I need to make the head a bit bigger (for stylistic purposes, proportionally its not that bad), the left leg needs a bit of adjusting (the thigh should be a bit thinner and I should fix the calf. In fact, I need to work on my anatomy knowledge on legs in general). But I think its the best pose that looks right.
What do you guys think?
ah yeah i combine my line method with my own experience with anatomy and foreshortening (for that i visualize the line to the elbow as tilted back or on a 3d plane), sorry i didnt clear that up. it wont work for every situation and its mostly for when you cant figure out how to connect the hand to the shoulder. (for bent arms like on hips or near the face)
something that also helped me are the line of action guides
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i dont use them for every pose i draw but for dynamic ones like yours it REALLY helps
you basically want your character to look like one fluid line rather than broken up into segments
Yeah the last one looks the best so far. 
Also a suggestion if you want to try this method. Try out just drawing the forms, no under skeleton (those ball joint lines).
I realized I'm more of a shape artist rather than a line one, and just drawing the shapes and forms I saw helped a lot. Before I used that ball joint technique and it seriously tripped me up with foreshortening and actually drawing what I was seeing.
Every artist is different though. Experimenting is the best way to find what works for you. You doing well on that front.
Also, also! Archery tips. Watch your arrow. It always goes above the hands, but only just (resting above the fingers on one, unless it's a compound bow), and held in place by two fingers on the dominate hand.
I actually do draw out the forms along with using a skeleton for certain parts (like the arm sometimes). I guess I could try using only forms at some point though.
So the bow has to rest like above the thumb and held by the index finger or something?
You don't want to hold the arrow's exit point, you just balance it. Otherwise that would hurt when it left the bow.
Explaining it is a little difficult. Here's an explaination with pictures to show the difference. You'll need to start at Method 4 for your Traditional Longbow.
https://www.google.com/amp/m.wikihow.com/Hold-an-Archery-Bow%3Famp%3D11
This shows the most common hand position, but I'll admit the dominate hand position is a little stupidly drawn in the example picture. Usually you'd pull the string back with two to three fingers with the arrow between the index and middle finger.
The other hand is spot on with the arrow balancing on the thumb, (you can also put your thumb against the grip like in my previous post and use your index finger).
Ah I think I get it. I think I understand how a bow is supposed to be held a bit better. Although, I really should have done my research beforehand.
I think I'll try redoing the sketch one more time with drawn out areas for the hands.
Okay this is the fourth one. The hands are hard to see through the sketch I know but I think I like this one better.
I took some liberties with this one too. I had the idea of making one side of the left leg one line and defining the other side and I just went with that for the rest of the sketch (Particularily the arms and the right leg. Though the right leg just ended up looking weird).
I'm more pleased with how this one turned out. It took a while to get it like this though. Lots of trial and error.