what sort of things do I need to keep an eye out for in models?

From this forum, I've learnt to break solids up into their surfaces and look for edges that are folded over.
but I still have some strange things happen like parts of models disappearing when preforming Boolean-unions.

What things have effect on Boolean function? (they seem to give me the most trouble.)
is there anything to gain from separating a solid into it's surfaces and running the "shrinktrimmedsrf" function over them? do the untrimmed points effect anything?

is there a "tips" post I should be looking at?

Cheers, Steve