Toilets
Toilets can be a real source of anxiety for some children. They can vary in different settings - some are self flushing, some basins have automatic hot water - these differences can cause distress for some children coming into a new environment.
If your child is not confident using "strange" toilets it may be useful to make a visit prior to starting at school so he or she knows where they are.
Your child may have been used to separate toilets if he is a boy and there may be a urinal. Talk about the etiquette of where to stand - usually if someone is there already, you don't stand next to that person but further away from them.
Talk through how to use the hand driers or paper towels.
If there are dispensers for sanitary towels or tampons if you have a daughter, then talk through with them how to use these machines.
If your child is not happy about the cleanliness of the toilets, you could also give them a small packet of wet wipes to use.