You're going to need to expand your knowledge almost every day if you want to become a great designer. You can follow blogs or follow your favorite designers on Twitter. Here are a few of my favorite places to start.
First, I'm going to recommend you get a Carsonified ThinkVitamin Video Tutorial Membership. It's about $25 a month and it'll get you hundreds of videos on web design topics put together by experts. (Cancel anytime.)
Learn about ThinkVitamin's Video Tutorials.