Tarrien
Never ever mess with fairy folk.
Never EVER disrespect the dead. Also never ask when or how you're going to die.
Those are two I hear of often.
As for never giving yourself a card reading- I've been scolded for this one by a "professional" reader and a few others... but I can't get readings that are nearly as accurate as mine are.. Part of it is I have a really hard to read energy...
This is VERY interesting to me as it's one that I've never actually heard before. In fact, I often hear exactly the opposite- the best person to give you a reading IS yourself.
From what I have always been taught, the Tarot is a focusing tool- it helps you to get past your prejudices or consider things you wouldn't have otherwise. Why would you expect this to work better if someone else is suggesting it to you?
Of course, this is a simplification (and a 'scientification') of the Tarot, but still... I certainly wouldn't consider it to be a problem.
As for the Ouiji board... Simply put, it's a tool. If you go into it believing certain things, you're more likely to get that out of it. It's just like anything else we use, no more inherently dangerous than an Athame and a Chalice.
Tarrien - I agree with the never disrespect the dead. Even worse, don't disrespect the living who loved those who are gone and grieve for them. (I'm looking at you, Westboro Baptist Church.)