I've found that if someones new and that they actually speak up and ask for help, they get it. Every time.
I've found that if someones new and they don't ask for help, the expectation is that they know what's coming.

Generally speaking, in dungeons, it's not much new. Dodge aoes. Deal damage. If something you can click on, click on it. It's mechanic heavy raids that may require some assistance to some, so don't be afraid to ask!