One of the fun things about reading Austen is that so many people have written about Austen. Her books are light on the surface (the plot is usually who will marry who) and dense underneath (history, class, gender, satire).
These days my favorite collection of Austen commentary is the hilarious and astute Bitch in a Bonnet: Reclaiming Jane Austen from the Stiff, the Snobs, the Simps and the Saps by Robert Rodi. I don’t always agree with Rodi but he’s fun to read, fun to argue with (mentally) and very astute. You can read my review of Vol 1. at Smart Bitches, Trashy Books. He covers Emma in Vol. 2.
What Matters in Jane Austen, by John Mullen, is a book of commentary that points out the social clues and the themes that appear in Austen. For a preview check out this article, “Ten Questions on Jane Austen”, several of which apply directly to Emma.
Study guides get a bad reputation because sometimes people read the guide instead of the book. Dude. Don’t do that. Having said that, I find the website Shmoop to be a great resource. I read it either after the book or alongside it and no matter how many college degrees I acquire, the authors of Shmoop always manage to point out something I’ve missed. Here’s a link to their page on Emma.
Just for fun: I like to read Austen while flipping through my beloved copy of The Jane Austen Book Club by Karen Joy Fowler. It’s a lovely book that was made into a lovely movie – and it involves the Sacramento Public Library!