Some that have taken a while for my autistic brain to work out:
If someone tells you something, don't share your own similar experience to show you can relate, NT people view this as one-upmanship
Ask people how they are/ what they've been doing, even if this is blindly obvious or they already told you their plans.
If you know someone for a few years don't mention it if they tell you the same anecdote several times and try to act surprised at the ending. NT people tend not to pay as much attention to what they're saying or remember conversations they had after a few months.
On a similar note, try not to mention anything about them they told you more then 6 months ago (eg. They don't like their cousin Simon). NT people might no remember telling you, so will find to creepy that you know.
Try not to correct people more then once in a conversation, unless it's a potentially harmful mistake. If they keep saying things that are incorrect, just nod, smile and disregard.
If someone offers you something you can't eat, say your not hungry, and eat after you've left. Don't tell them you don't like it or ask for something different.