Woo...! That's a very large image! If you have access to an image editing program of some sort, it would be good to shrink it down so it doesn't exceed 800 pixels in width (the board max to prevent page stretching).
But anyway! I did some redlines for you which I hope will help.
HydraTamer_redlines1.jpg [ 40.26 KiB | Viewed 3960 times ]
Something I noticed is that the head seems a bit small compared to the body and also that the hind leg seemed a bit too wide or thick or whatever you want to describe that as...! I drew a sort of rough sketchy thing of the underlying skeletal structure which I referenced from a dog skeleton. It always helps to learn about what's going on under the skin, so I definitely suggest looking at the skeletons and muscle structures of various animals so you can apply that knowledge to your dragons.
Generally, the uh... 'elbow', knee of the hind legs, and deepest part of the chest seem to line up horizontally in animals. Forelimbs also begin *before* the ribcage; they are at the front of the body with the neck uh... 'coming out of' them so it goes neck, forelegs, chest rather than neck, chest, forelegs. Yes?! o_O
Uh...! I also did some some vague lines as a suggestion for the positioning of the wings:
HydraTamer_redlines2.jpg [ 40.02 KiB | Viewed 3962 times ]
I'm not sure I can really say much about this that already isn't explained just by the lines themselves... I didn't go into detail at all obviously and just drew the basic shape of the area the wings would consume... That bit with all the lines in it in the back is supposed to be the other wing, just in case that isn't clear. It is a rather vague image, after all. o_O