We went thru this...the best thing for your son is to visit the school when the teachers, principal, etc., are all there and talk to each one. Don't just visit an empty building!! Show him the little "cubby" or whatever they'll use for coats, etc., the bathroom, water fountain, cafeteria, office .... EVERYTHING!!! If he'll be riding the bus, introduce him to the bus driver; drive the route and actually go to the school and park where the bus would park and walk the route into the building - tell him to NEVER walk off the path and go straight into the building. Do the same if you'll be driving him.
In other words, just familiarize him with everything!!!
As for communication - make sure the teachers have phone numbers, email addresses, etc. so you can stay in touch. I know for our school, each teacher sent out a short little blurb every Friday so we knew what they would be working on. If the teachers don't do this maybe suggest it to them as a way of letting parents know what they'll be working on. At this age, especially, we can't rely on the kids to bring home papers that parents need to see.
Also, can you volunteer at the school? Maybe not just in the classroom but maybe the playground, cafeteria, etc.? It was really helpful for my kids to see me periodically thru the day since not only had we switched schools but had moved as well and it was a very difficult and emotional move.
Good luck!!!