Personally I've never found a single guide that you could hand to someone, but if you're coming from a background of HTML and CSS then you should pick up formatting rules pretty quickly - they're essentially the same, but implemented via a GUI rather than explicitly specified selectors and tags. The key for me is to just pretend that none of the explicit styling options exist - so no use of Bold/Italic/Centered/Whatever buttons, and instead turn on the styles pane and apply all formatting from there.
And I've yet to find a guide which instructs on how to set it up properly, how to share styles across documents etc. Do you know of one?
20 years of writing HTML and CSS has spoiled me; many times I'm using Word and thinking "I could do this with one rule in CSS" (often some crazy positioning nonsense with images/tables). If only!