I have always talked to DS4 very directly. I think my mind works in many ways just like his (sometimes I wonder if his Asperger-like traits come from me?) ... I take things literally first too and then I have to MAKE myself understand things the way others do. So to me it's been a natural thing to talk to him very directly ... I've had some friends tell me I talk to my son like he was a dog ... And I just tell them ... maybe ... but IT WORKS! ... I just use a lot of DOs and DON'Ts and direct verbs and it seems to do the trick. He won't follow 2-step commands someone gives him, he won't even follow 1-step commands many times ... but if I translate the multiple-step command into our private "dog language" he WILL do what's asked of him.
Now, obviously, I am not comparing my son to an animal ... don't take me wrong! But it is that simple direct kind of language that he responds to the best! He has an amazing vocabulary that he uses but I can't use it back on him. I have to keep it simple.