When talking to an autistic child, these must be kept in mind.
Come down to the level of the child as it is easier to maintain eye contact.
Speak positively. For example instead of saying do not take my things, say hands quiet or for instance instead of saying do not leave this room, say stay in this room.
Be specific in your praise. Instead of saying good boy, be specific and state good listening, good writing, good sitting, good stringing beads.
Provide adequate information. For example, instead of saying we are going bye-bye, state we are going bye-bye to hotel.
Give a choice and ensure the choices are readily available. Would you like to listen to music or go on the swing?
Label feelings. I am sad because the vase broke. I am happy you are sharing your things with Isha.
Meaningless threats such as I will never speak to you, hold no worth. It is vague and cannot be enforced. Instead tell the child what to do such as clear up and go to bed.
Be very clear in what you want the child to do. For instance I gave my son a sheet of addition sums and told him to do it. He had done all of them wrong, in an illegible fashion. I had to rephrase it to try to do the addition right and write neatly.
Teach them to obey certain commands such as wait, stop, out of bounds, hands to yourself.
Teach an autistic child to listen, either by social stories or making him follow simple commands initially.There are some interesting games in the official website of Disney, like the Higglyball game and Jojo circus