Here are some points you should always consider when you start to design stuff. Some of these really apply for all, like light, color and perspective.
If you come up with more, feel free to add them.
- profession or title
- social rank
- physical condition
- mental condition
- carnivore, herbivore or omnivore
- how gets food/catches prey
- main materials
- purpose of the object
- powersource and material it uses as energy
- user interaction
- unique or for reproduction
- relation between shapes
- focal point
- colour contrast
- what's happening: who, when, where and how?
- emotion in the picture = faces + body language