The most important thing you should know is that patent or IP firms are looking exclusively for students with a "technical background." Technical background means an undergrad degree (and, it helps, a graduate degree) in a hard physical science or engineering. Without that background, it would be generous to say that a career in patent law is a long shot.
That being said, I'm taking patent law now (primarily to round out my IP education), and the class is full of students who already know it. Most of them have already been patent agents, or had their summer jobs doing patent law.
I picked up Schechter's Principles of Patent Law. It's been reasonably helpful. It's only about $36.