Probably been said already but
DON'T waste time and energy comparing your child to other children in their class - there is always likely to be some kids who are better than yours at some things.
DON'T get involved with parents who want to start bad-mouthing or complaining about another child/parent - if they want to do that let them, don't let them make the bullets and hand you the gun
DON'T always think that YOUR child is the one who is 100% guaranteed to tell you the whole truth, and other people's kids are the liars (or even the teacher for that matter) - a tendency to disbelieve some things and ask for the other party's side of the story is a healthy one IMHO, don't jump too rapidly to their defence, you may sometimes get egg on your face when your little angel's halo slips - I have yet to meet a child who does not have the capacity to be economical with the truth as it pertains to them!
If you expect draconian punishments/sanctions for other people's kids misdemeanors, then be prepared to accept the same draconian punishments/sanctions for your own child's failings.
DO appreciate that ALL children are different and will achieve things at different ages and stages, a child who reads first might be a child for whom maths is not so easy, or a child who is fabulous at football may really struggle with reading
Don't always be there to catch them when they fall (metaphorically speaking) kids can only grow their resilience if they are allowed to take risks and make mistakes - the best lessons we learn in life are when we have had to handle the results of our mistakes/misjudgements ourselves, and have learned not to do it again. A Confucian saying is 'I hear, and I forget, I see and I remember, I do and I understand'