Agent or Object?

                                    
           

                                              
Here's something to consider: could your autistic character be replaced by a teddy bear that speaks lines when squeezed, without meaningfully changing the story?
                          
Or, to put it another way: Does you autistic character actually DO anything?
                          
Sometimes, when writers try to write an autistic character, the autistic person just plays an extremely passive role in the story. They do what they're told. Sometimes, they look happy or sad. Their peculiarities encourage the non-autistic characters to think, and inspire them to learn Big Life Lessons. But mostly, they're carted around from place to place like a doll.
           

                          
In real life, autistics are people, not objects. While some of us may be prone to passivity (especially if our families don't encourage us to gain assertiveness skills), we typically do things, want things, and have our own ideas. Besides, that's what makes an interesting character.
                          
An interesting character is someone who wants something, and works on getting it.
                          
Let's look at some of my characters as examples. (Feel free to add your own examples in the comments.)
                          
Claire (Silent Voice) wants to create an adult life for herself. That means fulfilling her dreams of becoming a professional writer, and maybe falling in love. She actively pursues these goals during the story, and this pushes the plot forward.
                          
Aurora (Thousand Dollar Friend) wants acceptance and community, even if this isn't explicitly said. While she is prone to passivity, it's portrayed as a character flaw. She also deals with various subplots related to other desires (including romance, control over her life, and pleasing her friends) over the course of the story.
                          
Glitter (Silent Voice) is a little girl with an emotionally abusive father. She could have become the "poor inspiring pretty little autistic doll," but she's far from that: she's a messy, artistic, vibrant little girl who is desperate for connection with other people. When she meets Claire and Claire's dad, Glitter practically clings to them and begs them to spend more time with her. Essentially, she tries to get what she wants. And her pleas to "come back next week" impact the main characters' choices.
                          
(Why are they all girls? Because I like writing stories about girls. But you can write autistic characters of any gender.)
                          


                          
In ever scene, ask yourself: what does my character want? What do they hope for? It could be a major goal (like starting a company or avenging their mother's death) or a minor goal (like getting food or going home because they're tired). Figure out what your character wants and how they will try to get it.
                          
It's a common mistake for writers to give motivations to all characters except the autistic/disabled ones. The "real people" do all the action in the scene, while the autistic person sits around like a decorative prop, only to mysteriously reveal clues from time to time through their dialogue or make problems for other people to solve.
                          
Only, that's not realistic at all. Autistics are people, not props. And we have reasons for everything we do, whether others understand those reasons or not.
                          
Even if the autistic character is peripheral to a scene, you can still hint at their lives and their goals. Let's use the Thousand Dollar Friend characters, and pretend that there's a scene where the main character talks to Aurora's dad while Aurora is nearby. Here are some good examples:
                          
I walk past the living room, where Aurora is rocking back and forth hunched over her phone. Based on the giggles and the cat sounds from the speakers, she's watching funny cat videos.
                          
I walk past the living room. Out the window, I see Aurora running through the yard with a bug-catching net, a determined expression on her face.
                          
I walk past the living room, where Aurora is curled up with headphones and a book with a unicorn on the cover.
                          
In all of these cases, Aurora is barely part of the scene, yet she's still clearly a person. We know she likes cat videos, bug catching, and reading fiction. She doesn't speak a word, yet she sounds like a real teenage girl, instead of a decorative object.
                          
In scenes where the autistic character is involved with the action, of course, then they'll be doing much more. I've included lengthier examples in my example handbook.
                          
Nothing is less compelling than a character who sits around waiting for things to happen all the time. Show your character making choices and pursuing goals, and the reader will feel much more invested in them.
                          
Want to hear more? Check out the example handbook! I've (figuratively) cooked up something special for you.