Non-human can mean anything. It can mean an elf, a tissue box, a dog, a rotting apple.
The first thing you should do is establish if this character is living or non-living.
Non-living characters can be human-made objects or a part of the natural world, like a rock or water. Most writers, when writing non-living characters, give these characters thoughts, motivations, feelings, and abstract thinking in order to let the reader make a connection to this character.
Most non-living characters cannot move on their own, but inanimate objects who become animate (Toy Story, The Brave Little Toaster, The Nutcracker) have much more freedom. Here are some things to consider:
- Can your character move? If so, how well? Where are they able to go? If a lamp is unplugged, can it still move? Skateboards can go downstairs, but not up without help. Dolls are not tall enough to reach doorknobs without getting a little creative. Rocks can’t move at all. Necklaces go wherever the wearer goes when worn. Shoes only see the ground and the feet/legs of other people. What your character sees, where they go, and whether they can move will affect their POV and how they see the world.
- Can your character feel? Do they experience emotions or are they nothing more than an observer? If your character experiences emotions, they’ll have motives, fears, and flaws too. Develop them like any other character. If your character is an observer who acts as the narrator, you’ll need to choose the right object to tell the story of the people it observes. If the story centers around a family, the object could be a candle in the dining room that observes their conversations at meals and during other times of the day
and then the candle melts and the story ends when it dies.
If you’re writing fantasy and sci-fi species who are similar to humans in that they create culture (religion, language, architecture, art, societal norms, etc.), go through my world building tag on the tags page and develop them like you would any other character. Writing a character like this is similar to writing or reading a human character who comes from a culture you are not familiar with.
But, there are also the biological differences that might make some of their cultural customs impossible to occur within our species. If there are any of these, they should be normal to your character. For example, if this non-human character belongs to a species that can fly, certain groups might have cultural customs that involve flying or wings.
If they’re not like humans, you’ll have to establish what your character is capable of and you’ll need to think about how they view the world. They might not be able to understand the concept of language, but they might still be able to recognize threats, emotions, and people. If they can’t understand language, third person would probably be best for POV and you probably won’t have any dialogue. You’ll have to rely on your character’s actions and observations.
One major part of writing a living, non-human character is the non-human part. Something has to set them apart from humans. They can be a separate species, a ‘cousin’ species, or a subspecies. When humans see this character, there should be something there to say this character is not human. Even if they look pretty similar to humans, other characters might be suspicious.