Remember to leave your pants on when you get changed for PE!
Seriously, I did lots of talk about how exciting it would be and how many new friends he'd make etc. Really talked it up. Then I was worried that I might have talked it up a bit too much so we had some chats about what to do if he felt lonely or worried. I talked a bit about how I felt nervous when I started my new job because I didn't know anyone and didn't know what to do and where everything was but now I have friends and I really like going to work (stretched the truth a little bit on this one!)
I made sure he knew what the drill was, i.e. this first week it's mornings only so after lunch I'll be picking him up. We visted the school a fair amount before he started - not formal visits, just walked up there and had a look.
I also realised that I project onto DS a bit. I'm shy in social situations and not great at making friends so my biggest worry for him is that he'll find it difficult to but I've come to realise over the past few months that he's actually quite confident and sociable so I need to just let him get on with it. And he's been in nursery full time for the past year so he really does know about asking to use the loo, sitting on the carpet and listening etc.
It was his first morning today and me and his dad walked into the classroom with him and helped him find his peg, and then he spotted his teacher so I basically said "right, there's Miss, off you go, have a lovely time" and he went off quite happily.
Try and project as much breezy confidence as you can and she'll pick that up from you. Good luck!