Developing a sense of proportion actually comes from a mixture of observation (learning to look) and practice (experience), although it helps to have a knowledge of structure, and there are various exercises that can help with that. It would be impossible for me to give you a template for every species, and even within a species there can be many variants – think the differences in the proportions of a dachshund and a greyhound!
There are, however, some general pointers on what to look for, and some surprising commonalities. Learning about proportion is best done from life. In working from a photograph you can inadvertently replicate a lens distortion (smartphones are the biggest offenders here), or the angle from which the photograph is taken can cause foreshortening, especially of the lower limbs if the angle is slightly from above.
To practise drawing, it does not matter what animal you use, you can even use a human if you look for a good lifedrawing class. The idea is to get a feel for ‘learning to look’. Once you get the basic feel you can start to sketch, draw and paint animals with more confidence.