Lay down big puzzle pieces and spray paint over them. Wait until they dry to take the off. These would make beautiful autism awareness shirts. Autism Speaks is bad news bears for actual autistic people! Cool shirt though.
If you want an adorable shirt that you can dress up or down and use for any season, you& love the DIY Lace Insert Button-Down Shirt tutorial. This is the easiest of sewing projects for beginners, and you can sew it with a machine.