Here are some of the (no longer) unwritten rules:-
1) I don't review things I haven't read - although I may make a comment if I've tried to read something but stopped because of the content.
2) I don't rate or review my own books (although I may refer to someone else's review or a straight description). How could I be even remotely objective and in view of this, how might readers perceive such reviews?
3) I can get very emotional about stuff. Being in touch with feelings is a useful quality for a writer. But in the end I always try and make a rational rather than an emotional decision. Do NOT shoot first and ask questions later. Regret is not a fun companion.
4) I always reserve the right to change my mind and I try to fess up if I was wrong.
5) Honesty is a good policy.
6) I despair about the fakery, witch-hunting, name calling, stalking, hate-filled behaviour that has been on the rise in the online book world. Wtf. Why do people do this stuff???
7) Know when to say nothing. Sometimes silence is the right response. Sometimes silence is eloquent and speaks volumes.
7) Be yourself - being someone else can be much harder to pull off.
8) Don't get stuck on past problems or mistakes - learn from them, apologise if necessary, and move on
9) Be nice. Most folk respond well to good treatment.
Feel free to add your own rules in the comments. In view of my number 6 above - here is a link to 5 tips for writers using social media from Nicola Morgan.