These would be my tips, but many may disagree.
*Always help out people struggling with an id if you know the answer and they don't.
*Always point interesting things out to people rather than keep it to yourself.
*If people are queuing for a seat DO NOT just sit there eating your sandwiches making them wait!
*Don't just sit there with your massive scopes/photography equipment taking up five seats.
*Don't walk up to hides shouting your head off, as if birds can't hear you until you're actually inside.
*By all mean discuss birds in a quiet voice, but don't sit there gabbling loudly about any old rubbish.
*Never stick your arms out of the hide.
*Don't sit quietly up one end of a hide while your children run riot at the other...
*...but also give children in the hide a bit of slack. Unless their interest is grabbed, there'll be no future generations with an interest in wildlife.
*Leave your arrogance behind. Just because people may not know as much as you do (or you think you do...) doesn't mean they don't have a right to be there.
*If you get sick of people being in hides, remember there's a whole world of birdwatching out there that doesn't include popular nature reserves! You can't really have the arrogance that you're a much better birder than the rest of the world if you never do any birdwatching outisde RSPB reserves...