The knack for all of us has been to know exactly what the place is like, exactly what will be done each day. Photos, maps, plans, diagrams, anything that gives tons of detail on what to expect. Without it, I can't go on holiday as it's too stressful for me, and dh and ds's stress levels go through the proverbial roof if they don't know exactly what will happen when.
I guess our holidays have worked because we're so similar in what we need, and don't stress each other out hugely as we know not to do the mad social whirl that others really enjoy/make decisions on the spur of the moment (er, do moments have spurs? Goodness, there's some strange expressions in language ), etc.
We've just had a holiday with friends, and we were fine with it until the friends unexpectedly invited their relatives over for a meal. We hid. We're adults and we hid . In fact, I went into the bedroom and burst into tears because I was so stressed out by it. They were nice people too, and normally I love meeting people if I know it's going to happen. We just weren't expecting it, so had already used all our 'spoons' for that day (google "spoon theory" )
Difficult, life with people on the autism spectrum, eh?