... I think common sense is the best guide, as always. ..
everytime i read something like that i am reminded of the signature quote at the end of emails i used to get from an old molecular genetics professor of mine, "common sense isn't" lol
in all seriousness, just try to be considerate, try to contribute more than you ask of, consult dr. google prior to posting as appropriate.
do not ask for or post scores of copyrighted non public domain piano works, and those that are public domain, refer requests to the piano street sheet music service if the piece is offered before posting something that can dilute the revenue for the site.
try to abstain from expounding on subjects you have little authority on or at least make sure you are passing along good info, i.e speak not what you know not of.
ask plenty of questions. try not to derail threads too badly or at least try to get them back on track.
look for appropriate sub boards/rooms for topic starts.
do not doulbe post in an effort to try to get a response , more reponses or reponds faster.
have fun. don't be too serious. don't be troll.
that's all i got.