Communication is key to all relationships. ASD affected children need more careful communication than you would have ever delivered before. Communication for them needs to be precise, structured, clear without slang/colloquialism/figurism. It's very similar with ADHD, it makes for less misunderstandings.
I've been told growing up 'Come here to I murder ye', 'Don't come running to me if you fall and break your two legs' or 'You look like a drowned rat'. We all learn our parents aren't actually going to kill us, they're just extremely annoyed at something we did. If we did fall from climbing a tree, they'd probably run to us. When we are caught in a torrential downpour, we physically dont look like a rat. To ASD children they will take the literal meaning. 'You'll catch your death of cold, if you go out in that' :)
Even when we think we do communicate clearly, it will take them longer to absorb and process what has been said. For our boy, it will take 10 to 15 seconds for him to recognize that you are speaking to him. Over time I've made myself (frustratingly at times) to say his name, pause and count until I'm sure I have his attention before telling him what he needs to do, or what I want him to do.
I know it's very difficult for him to look me in the eye sometimes. When I notice it, I tell him 'good eye contact'. If he's not looking at me and I'm not 100% sure he has actually heard me, I ask him to repeat what I said. At times it can take a lot of patience.
Tone of voice is something almost alien to him. In the past I've spoken, repeated what I said, repeated it again and got no response. I made the assumption he was just ignoring me. My tone and volume would change and all of a sudden he jumps with fright because I'd shouted. He couldn't hear the subtle changes in my tone over repeating myself again and again. It was the shout that would get a reaction and it would be the wrong reaction.
Facial expressions they struggle greatly with. Whether it's anger, frustration, sadness or joy. The emotions we all wear on our faces aren't read. When this was highlighted to us, we spent a Summer working on face pics and emotions to coach him in reading them. Now, at the minute with almost everyone wearing face coverings and masks it's a very unusual time. My heart goes out to the children.
Use visuals where possible or necessary - as an example - we have on in our bathroom, it starts at the door and finishes with turning the lights off - with an appropriate image for each required action (flushing, washing and drying hands etc). It saves a lot of heartache. In school our fella has a timetable taped onto his desk, so he knows what is happening each day and also what to expect next.
They won't get long lists, if you send our lad into his room, to pick up toys, tidy the bed and put his laundry in the basket, he will get into the room and forget. Use the 'First, do this, then, do that' rule - two items is about all he can deal with. I'd also suggest to use that guide when you want your child to do something - 'First, you finish lunch, then, you can play'. It helps our fella focus a little more on the task in hand.