Before teaching in school, I worked in several group homes for autistic and medically disabled folks...
Kids are kids. Read IEPs and 504s first for seating issues, then the fine points. Do a variety of projects, some messy, some neat, 2D and 3D, every kid will find their niche. Be ready to simplify, but also to challenge. Some kids will struggle making a line, others may surpass your own skills.
As soon as someone tells you not to do a certain kind of project for special needs kids, doubt that advice deeply. If they are ALL autistic, there may be a few true-isms, but even there, skill sets are broad.
If any come with an aide, USE THAT RESOURCE, they hate to be board too. If you work in a district that is "specials focused," the skills you use there will FULLY apply and help you deal with ANYTHING in public schools. I know I am a better teacher because of my years working in group homes, and there may be one in your local neighborhood. I highly recommend education majors in college seek out such jobs to help hone their skills.
"But what about students that are severely disabled? Surely they need to do something different?!"
NO. If you have a student with "special needs" and they are integrated into your "regular" class, They should use the SAME materials, and do the SAME lesson, UNLESS SAFETY IS AN ISSUE.
So when my class is doing gridded self portraits, my special needs students do what they can at their level of ability. Maybe they just draw a face on paper and color it. Their aide can prompt them to include similar features to their own; freckles, glasses, ponytail... Maybe the aide can draw a face very lightly in pencil and that child can trace. Maybe a student will just be able to draw head shaped circles by themselves, and maybe it's hand-over-hand for a severely disabled child who is able to choose colors.
When painting, having all the available colors might be fine, but for some, one color and a brush is enough for an experience. EVERY LESSON YOU DO can be simplified to the bare essence of what is to be learned.
In some cases my special needs kids will finish far quicker than my other students. So when my class focuses on 1 thing, my specials need to do it about 4 to 8 times 'cause they are so fast. So sometimes they do the first or last one on the "good paper" and the others on free copy paper I sneak from the office as practice. If class is too long for them, like for block scheduling, talk with the aide, and see if at every half-way point they can go for a walk around the building, or go in the hall to stretch, get a drink, some little break may help. While in the hallway they could complete a simple task: Find 8 things that are red, or 6 square things, cubes, rough/smooth, etc, exploring the art elements with each visit.
When you have a gifted student in your class, you know to push them a little harder than the others. Show them a little 2 or 3 point perspective while the others struggle through one point. To show them how to stipple or crosshatch when others struggle with just making a smear for a shadow. Add background details, highlights, textures so that you can meet their needs, so they have pride in their gifts and soar.
Here's my one "true-ism" for specials: Treat them just like any other kid but be ready to modify to meet their specific needs... as we do with ALL our students... and once in awhile, one will surprise you.
Form more about the needs of Autistic Students, please visit HERE.
Below the images I have a letter you can give to your aide in helping with your special needs students.