What should I be looking for if I must write notes on the Elements of Style, like language, organization, diction, or any other stylistic devices?

I'll give you a basic idea of what each of these elements
of style include - and hopefully you can take it from there.  I'm going to take them out
of order because I think it might make more sense this
way.

Diction is word choice. 
Here you want to look for any vocabulary that holds a very specific meaning or
connotation.  Consider the difference between describing a child as
"chunky" or "husky" compared to "fat" or "obese."  Although each of these words has the
same basic meaning, there is a reason why you might choose one over the rest depending
on the message you wanted to relay.  (Do you want to paint the fat kid in a positive or
negative light?)

Language (to me) could mean a few things
as opposed to just diction.  With language I would look for figures of
speech or figurative language.  These are
similies, metaphors,
personification.  When an author is being figurative this
means he or she is using non-literal descriptions for things to emphasize something. 
"I'm so hungry I could eat a horse," is a common figure of speech.  I couldn't really
eat an entire horse - duh - but it a huge animal that is compared to my huge
hunger.

Organization is a
broader look at either a section, chapter, or the novel as a whole.  I suppose in this
novel you might want to ask, Is it organized logically?  Chronologically?  Does it
follow a basic story line (exposition, rising action, climax, resolution)?  Are there
flashbacks?  How many plot lines are going at once?  Where do they
intercept?

One other major element of style that is left
out of your list is tone or
attitude.  I think it is pretty central to how you look at
the rest of the above.  Ask, What is the author trying to say (what message is being
sent) and what tone is used to speak that message?  Why and how?  This is a central
question to style analysis that you can use to incorporate all these other
elements.