This is a classic and well-respected work on treating autism, and yet the floortime approach is really only going to work if your autistic child has some interests that you can be part of. If your child is self-stimulating on a blinking light toy, or perhaps by opening and closing a cabinet door repeatedly, it will be hard to interact with him / her. In my experience, the child won't appreciate efforts to, say, hide a toy in the cabinet and find it together. You and your child with autism need to start at a more basic level: see Motivation and Reinforcement: Turning the Tables on Autism for what is, in my opinion, the most helpful approach for even severely autistic kids.