On the morning of the big day, accompany your child without making too much of a big deal out of it. If you wax lyrical about how great school is too much, you might end up putting them off!
Once you get there, follow the teacher's guidelines on shoes, clothing, etc. Go to the classroom with them, say goodbye, tell them you'll be back to collect them in the afternoon and leave quickly. Don't let the separation drag on: if your child is upset, it will make things worse.
Although it's diffcult to deal with, don't worry if they begin to cry. The tears soon dry once parents' backs are turned...
In the evening, let them unwind and talk, but don't bombard them with questions, even if you're dying to out how the big day has gone.
It's a good idea to make them associate their first day at school with a pleasant surprise. The German tradition is to give children a cone filled with sweets and toys to mark the big day.