The thing that autistic children typically have the most issues with are the rules related to being a part of the society. It is not something you can learn in a special class but these are rather things you obtain through subtlety and following your parents’ gestures. If you are a boy and your dad always waits for a woman to enter the room and only then he enters it himself, then most provably you’ll be doing the same thing.
But in the case of autistic people they don’t really catch up on those subtleties, which may be difficult for them. What is the solution? Well, if you catch your child in a weird social situation that could be solved better, a good idea is to talk about it and walk your child through what has just happened and why, and what usually a person will do in such situation, so they can remember that for later.
You can also buy them some books about behaving in society for younger or older children, depending on the age of your offspring. An encyclopedia of savoir vivre may be an overkill but a little book intended for children about why should you behave in certain way may enlighten your child. There are also special books of this kind for autistic children. It could be an interesting idea to look for them in the Internet or local library.
You can also ask your family and your child’s friends to be empathetic towards his behaviour but at once to talk to him if they think something could be improved. However you have to remember that everyone has a different idea of savoir vivre so maybe sometimes these things should be consulted with you beforehand as not to make it all messy for your offspring.