I just finished reading The Killing Zone by Paul Craig. Be sure you get the second edition; the first edition is nearly 20 years old now and a lot has changed since then. Just before that book, I had read Situational Awareness, also by Craig. The books are very similar: both are largely made up of transcripts of NTSB and NASA investigations and reports of various accidents or close calls, followed by discussion. The Killing Zone builds up its thesis over the entire book but really brings it all home in the last chapter, and has helped convince me that I should go for instrument and perhaps even commercial ratings sooner rather than later after I pass my checkride. I was already planning on continuing to fly with my instructor every few months, knowing that I’d be going for the instrument rating eventually, but The Killing Zone makes a compelling argument that continuing to learn and hone your skills for those higher ratings can really make a big difference in how safe you stay as a pilot.