My son was evaluated for Autism at 3 and they said he did not have it. At 5 he was diagnosed with a form of Autism (PDDNOS). I can understand SO much b/c he was so hard with all of his OCD issues. Like the way his shoes were put on. Right sock, left sock, right shoe, left shoe. If you did it differently he would take them off and throw a fit. There was the need to go first at EVERYTHING... not just a typical kiddo need, but to a pervasive degree. There was the need for EVERYTHING to be blue, again, to a pervasive level.
One thing that was hard for me was the times when I would have to break his rigidity. His behavioral psychologist encouraged me to do this b/c in the real world not everyone will accommodate this, which she is correct. I would pick my battles and only focus on one thing at a time. He still struggles with the going first the most.
One of the biggest problems was that he had a favorite, to a pervasive level. He had a favorite grocery store, a favorite Mc Donalds, a favorite Wal Mart (despite so many of them looking the same, he knew he difference), a favorite road, etc. He would fall apart when I turned right on red b/c red means STOP.
What saved me was social stories. You can make these yourself on the computer. Heck w even drew some together and he helped me draw the pictures. They don't have to be fancy, but they convey a message in a way the kiddo can understand. There are some rules. 1st, it HAS to be in 1st person. Ie. My name is John, (meaning John is your kiddo) I like this.. I do that... etc. If you try to make it a story about about some other kid, the kid will miss the message and the generalization that it is a problem he is learning to fix.
Here is one I did with my son after he chose a favorite friend out of my friend's 2 kids. He was excluding one and not to be mean, but b/c in his mind the one kid was his favorite:
My name is "Billy". I like to go to Sarah and Joe's house to play. One time I went to play with Sarah and did not allow Joe to play. That made Joe sad (important to convey how it made "Joe" feel). Joe likes swimming and so do I! Joe likes to work on the computer and so do I! (important to convey positive things about Joe) Next time I go to play, I can play with Joe and Sarah. It makes Joe very happy. Now we can all be friends.
We made this story together and drew pictures and it really helped paint a picture of how play time should be and how to include everyone. It was still a struggle but WOW it helped!!!
Feel free to PM me about social stories as I have made a lot of them and they are SO SO helpful with rigid kiddos. I have made them about going to school, standing in line, playing, being embarrassed, etc.
Good luck!!!