Sorry it's a bit messy, I went pretty quick. I can always go back and fix details if it's not clear enough. 
Also the pose is actually impossible I realize now but I wanted to show the front hoof and back in two positions, so oops. 
Anyways, really neat creature here. ^_^ I've divided it up into a few categories marked as letters so I can explain what I did. ^_^
I left out the antlers because there wasn't much room and they were ok anyways.
a) Head
Not bad in terms of shape actually. :3 Only thing I would point out is that the eye could be placed a little further away from the front, since deer are prey animal and they're eyes are on the side of the head, not facing forward like a dog or cat's. Also, the nose is more like this: {X}. It blends into the snout a little more than a canine's and the nostrils are larger and almost parallel to the mouth. But overall, a pretty good head, just needs to be a bit smaller compared to the body.
b)Neck
The biggest problem is just that it isn't long enough, and is arched the wrong way. Deer have weird, upward curving necks that are quite long and thin compared to the body. Personally, I think it's the hardest part to get right and in proper proportion. However, you did get the chest right, with it sticking out in front of the point of shoulder, so good job.
c)Legs
The main problem with these was just the length. ^_^ Deer have long and skinny legs. For the joints, the only way to improve is to look at a reference picture or your own arm/leg. Deer basically stand on tippy-toe - for the back leg, think of your heel as the hock and the tip of your toes as the hoof. Front leg, same kind of deal, except your wrist is their knee. As for the hoofs, yours are actually not bad in general - just remember that unlike larger ungulates like horses or cattle, deer have pretty skinny, sharply angled hooves. And you did make the back legs longer than the front, which is common in most small deer species and is something a lot of people tend to forget. ^_^
d)Body
Not much wrong here, just remember that deer have big, round bellies and often slightly arched backs.
e) Wings
Ok, tbh these are not my forte, but I know some basic sketching technique so hopefully I can kind of help here. You did a pretty good job of having the different groups of feathers, the only thing I'd recommend if you're going for a more realistic wing is the remember where the joints are and how they bend. I use the old wing-is-an-arm trick to help me with that, where the tip of the muscle-y part of the wing is your index finger and it basically just goes down to the shoulder. Of course, if you're going for stylizd wings, this doesn't really matter.
I left the tail pretty much as-is because it would work as a display tail, but for a more flight-worthy tail I would just flatten it out laterally.
Ok, hope all this helps and makes sense.
Let me know if I need to explain something further.
