
Getting books about the anatomy (preferably with pictures!) of the animals you are interested in is a good idea.
Also books which explain in simple terms perspective and proportions.
Generally, perspective and proportions are the things people have major problems with, so practicing that is good, (with anything, doesnt have to be an animal!).
Other things to look at are light and shadow. Whenever you draw anything , set in your head where the light source is coming from.
Practice by drwing a cube, draw it several times and each time alter the light source, and therefore change the shadowing.
Em