A friendly chat with your ds's future class teacher and TA, a few basic questions (previously filled out on form in our case, they were just checking the info was right) about allergies, nicknames, etc.
In dd1's case, a trip up to her bedroom to show her more important cuddlies to her TA, in dd2's case tea and cakes (pretend ones made by dd).
It was really just to help the child feel more secure when they came in to school, and to give the teachers a feel for what 'home' means to the child - in other words, to improve relationships and communication. Nothing more (and they didn't care whether the house was tidy - luckily!).