Get a Whiff of This by Sandi Metz

Most code is a mess. Most new requirements change existing code. Ergo, much our work involves altering imperfect code.

That's the bad news.

The good news is that every big mess consists of many small ones. Certain small problems occur so frequently that they've been given names, and are collectively known as "Code Smells".

This talk shows how to take a pile of perplexing code, identify the "smells", and surgically apply the curative refactorings. It breaks a messy problem into clear-cut pieces, and proves that you can fix anything without being forced to understand everything.