just go by argument topics
Best way to do this is really just to look at the essay question, and jot down your first responses - for example: (this is my typical line of thinking)
"Explore the values raised in The Shipping News"
1) For starters, the author is like this fully hardcore Greenpeace activist, therefore the book stands as a literary "STOP KILLING NORTH ATLANTIC SALMON!" tribute
2) author's belief that local communities should be preserved more, because they're the only ones that properly appreciate salmon in their natural habitat (ie alive rather than dead), hence plotline
etc etc
starting easy then finding techniques to back it is much better than trying to dive straight into "the use of ___ is evident through the author's employment of rahrahrah..."