I found this really accessible: it's written like a serialised magazine column with each chapter covering a single concept (e.g. metafiction, intertextuality, unreliable narrator), introduced by an extended illustrative quote from the English language literary canon and covering just enough detail in 4-6 pages. Very easy to dip into, which is good because I sometimes struggle to read nonfiction in longer sessions.

Thanks to @Siobhan_M_HQ@beta.birdsite.live for the recommendation (though she will never see this...)