Giving specific feedback is important for a child with ASD as they typically take statements literally.  An example of specific feedback is, "I like how you came in and sat down  quietly."  Rather than general praise which can be, "good job" or "thank you".  

Giving students interminttent positive feedback is also important.  The classrooms where students succeed the most are using the rate of reinforcement to correction at a 4:1 ratio. That is, at least four positive communications are given for every one correction.

Ten Proactive Strategies for Teaching & Maintaining Positive Behavior

Another important startegy is offering choices. This will help to avoid power struggles and give the illusion the student has control over their school day. Choices can be offered within your control, such as, "Do you want to do 4 problems or 5?" or  "Do you want to do this first or that?".

Choice Example Video