As the title states: if you have a guide book to reading an author or a specific work, should you read it before, after, or alongside the work itself?
I've wondered this for a while in a general sense but I'm asking it specifically now because I've just purchased a copy of Dante's Divine Comedy (Steve Ellis's translation) and Prue Shaw's Reading Dante: From Here to Eternity and I'm unsure which to read first.
I've never bought a companion guide for a book before and my gut feeling is that I should read the Divine Comedy first and then the guide, and then perhaps the Comedy again.
Is there an accepted rule for reading order when it comes to guide books or is it largely a mix of personal preference, purpose for reading (study/pleasure), or dependent on the work in question?