Contact an Autism society in your state they will have lots of suggestion. In the mean time use lots of visuals when you talk, signs and pictures. Try to gain their attention with words like looking and listening while pointing to your eyes or ears.(it works well with all kids.) Don't make a big fuss of them let them have some space if you find they don't handle big groups or loud noises, use smaller groups more frequently and always move that childs group to the quietest spot in the room. Try not to have to many stimulants in the room eg. tags they may fixate on and above all talk to the parents most have a great knowledge of the condition and will freely give you all that you will need.
You'll be suprised at how a small step for most kids will make you feel like, you and the child have moved mountins they can be so rewarding.