The first step is to collect relevant reference images to study the animal and then make a rough sketches keeping in mind these points.
a. Form - Overall shape of the creature.
b. Structure - Identify how different parts of the animal function.
c. Anatomy - Learn how the muscles and bones work together to form the frame of the creature
d. Locomotion - Observe how the animal moves around and the nature of the movement. Eg: Sluggish and slow or Fast and light.
e. Design details - Observe the various aesthetic points of the creature. Eg: Yellow of the beak.
More Examples:
