Originality

It's important that you have original ideas for creature rather than reusing things like wyverns dragons or griffins. Originality is a very important part of creature creation, copyright issues aside, normal fantasy creatures no longer grab the attention or interest of a reader as much as they used to. because of this, it's a good idea to come up with something nobody's ever seen, something amazing, something creative and visually pleasing, or if you write horror or mystery type books, gruesome and eerie or uncanny, but remember to keep it as simple as the idea can be if you can.

Simplicity is key

For something to be simple, it has to be easy to remember it's name, not too difficult to recall it's appearance and original. For beginner writers, something such as simplicity is important. in order to prevent someone from being overwhelmed by the facts and specifics of a creature, simplicity is key. if it's simple its easy to draw multiple times, easy to recognise, but not simple enough to be called unoriginal or boring. of course, all creatures need some form of detail and complexity, the point is not to overwhelm the reader with too much of it!

Environment matchup

The creatures features, abilities, preferences, diet and approachability can all be decided simply by the creatures natural habitat. you wouldn't spot a sand creature in a desert area to have gills, so why should it? creatures in water rich areas should be more likely to have fins or gills than spider legs and fur. think about the plants and bugs in the area, how might a creature adapt to living and thriving in that specific environment. think about existing animals and how they adapted, some have camouflage while others have poison spines along their backs. also think about the level of aggression and diet this creature possesses.