http://www.3dtotal.com/team/Tutorials/amouse/amouse01.php
http://www.3dtotal.com/team/Tutorials/makingofshark1/makingofshark1_1.php

Decide on an animal. Get lots of references for that animal or a very similar one. Look for anatomy images if you can find them and also for regular photographs of the animal you're modeling. You will find that often anatomy images show you more muscles than actually show up on the animal when fat and skin is taken into account, so those should be used as guides but be prepared to soften areas.

3D Studio max tutorials are usually the easiest to convert to other applications, so hunt those down if you can. If you can find ones specific to your app of choice, great!

Two useful books:

Animal Anatomy For Artists by Eliot Goldfinger
An Atlas Of Animal Anatomy For Artists by Ellen Berger

Both have excellent illustrations that can be used as modeling references in conjunction with real photos.