I commend you on for coming to ask about this. Really, That would be helpful for others to get an idea of how to interact with autistic people of all ages.
Autistic people are just like us. We may view them out of the norm but it does not mean that they should be treated differently. Treat them as you normally would do to others.
Although, I'd advice you that if you ever happen to see an autistic person doing such said behavior like, not looking at your eyes, or doing such tantrums, may lie down inappropriately, scream, or cry or whatever it is - DON'T give stares of disapproval, shaking heads and accusatory looks because that also can create an uncomfortable situation. Speaking of that experience, I've often got that from others whenever I'm out in the public with my son.
Don't talk down to them. Talk to them as you normally would do to one another. Give a smile, shake hands with them, be proper.
You'd be surprised how open they can be at times.
Also, This is a blog that is well worth reading. It will give you an idea and such into depth of Autism Etiquette --
Water, No Ice Autism Etiquette
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“Tough girls come from New York. Sweet girls, they're from Georgia. But us Kentucky girls, we have fire and ice in our blood. We can ride horses, be a debutante, throw left hooks, and drink with the boys, all the while making sweet tea, darlin'. And if we have an opinion, you know you're gonna hear it.” - Ashley Judd