I can’t emphasize enough the importance of being realistic, even/especially in fiction. A writer can never be too informed. Remember, Knowledge is Power.
You’ve probably also heard the saying “write what you know”. Now, to the science fiction or fantasy writer this phrase may seem worthless. Write what I know? How can I possibly learn all about or experience things that don’t exist? Even fantasy can be built upon a realistic foundation, and there are endless resources to build that foundation with.
Reading what other people have written to get a feel for a genre is always helpful, and discussing things with friends never hurts either. Is your character a master of disguise? Pick up a book, learn how it works. Are they a thief? What are some tricks thieves use? How does one pick a lock? What’s involved? Are they a knight in shining armor? Just how easy is it to move around in a suit of armor? How about lifting those huge swords? Can they get on a horse without help? PBS has some great programs just full of information, as does the Discovery Channel and Animal Planet. Your local library is invaluable, and of course endless information is just a Google away.
Pay close attention to animal anatomy for more fantastic creatures. Naturally you have to fudge things to some extent sometimes for creatures that really don’t exist, but it’s educated fudging. This makes it more realistic, even though it isn’t real. For example, one of my RP characters was a winged centaur (or rather a relative being half elk instead of horse). While he turned out to be an absolutely beautiful and amusing fellow, he was also over 8’ tall at his head and weighed over 500 lb. Pretty as those feathered wings were, there was no way he was lifting himself off the ground, they weren’t big enough. He could leap and glide a short distance, but if the party had to climb a rope or cliff he was utterly useless - which was great fun to play out. Limiting characters makes them more of a challenge, the more they struggle the more they grow and the more fun they are, but I’m getting ahead of myself here.
Physiology, psychology, weaponry, philosophy… The world is at your fingertips. All you have to do is look and/or ask. Having easily accessible reference is important for any writer and/or artist, and having books on hand is the most convenient method for any creative person. It’s much easier to have information on hand than to remember it. I personally hate having to return Library books, because as soon as I do I need it again. I have shelves of reference that I am eternally thankful for and keep returning to again and again. Especially since, while the internet is a valueable tool when it works, a useful website may be there one day and gone the next.
Ask questions and look into all the available sources to find the answers. Sometimes, you’ll find answers to things you hadn’t even thought of, and often your research will end up inspiring you! There’s many writer’s guides available, based on research other authors have done to help folks out. The more you know, the more realistic your story and more involved your audience will feel.
This works for Art as well. Pay attention to the world around you, notice how things work and look. It’s important for a character, picture, place, world, to feel somehow natural regardless of the style. Create a “morgue” (yes, that’s the actual term) by cutting out magazine pictures that remind you of characters, landscapes, items, or have positions you find difficult to draw and keep them in a handy binder.
Sometimes you won’t be able to find the answer you’re looking for. Make a decision based off of what you do know. Go with your gut and what feels right to you. It is *your* character, and in the end only you and they will know what’s best.