#1 One of the biggest tips I can say is, ask ask ask!
Ask the family members, Mom, Dad whoever or even the child or person with autism, if you can, and find what they might particularly need to make the environment comfortable for them.
#2 Consider their diet.
A lot of children/adults on the spectrum require a gluten-free casein-free diet some even remove sugars but that being said a lot of them have particular food choices that they want to eat like chicken nuggets or peanut butter and jelly sandwiches. For our son he is actually gluten/casein and some other grains free so he tends to eat proteins, fruits, and sweet potato chips! Each child can be different so ask, I know cooking is hard during Christmas but it doesn't take much to throw some chicken nuggets in the microwave or make a peanut butter and jelly sandwich if that's what it takes to have everyone be comfortable and not left out or hungry.
#3 Explain to others what autism is and what it isn't.
Now adults and children on the spectrum have varying different abilities, some don't make eye contact some are nonverbal some like hugs some cannot stand that sensory input. Explain so others are prepared when the behavior of the adult or child with ASD seems very different. Explain in a age appropriate way why they are different. (Like "their brain is wired in a different way and that is why he doesn't hug because it actually feels painful"). A lot of times just explaining to people or children helps them know what to do and how to respond appropriately to the ASD child or adult.
#4 Consider a quiet place to retreat.
Not saying everyone has a room in the house specifically for sensory overload but, if you can, have one bedroom reserved for them to be able to go in when things get too hectic too loud to much overload that they need a calm quiet place to regain composure. For them, that helps them know they have a safe calm place to go to and it will help the parents/caregiver also know they have a place to take them to help them regain that control. This room doesn't need anything fancy maybe curtains drawn or blinds closed not a lot of obstructions on the floor, no bright lights/no loud music. You could even post a piece of paper on the door that says "calm room" and show the child or the adult where to go when they need it. Again, just ask the parents or the child what they think will help. They’ll probably even bring along a weighted blanket or some noise canceling headphones to help out!
#5 Remember this time is about being with your family.
Just remember to love and be patient and accept that things will not go as planned and be okay with that!!!
Do your best and try not to stress!!!
Have a very God blessed merry Christmas, to all of you from all of us here on AutismRoad.