If you've learned the basics, the next step is to exercise the basics on small but increasing challenges; so that you can mentally decompose large challenges like GitHub projects into attackable pieces. A year ago, I would have suggested the Euler challanges, but today I'd recommend the Matasano Crypto challenge. Why? 'cause chicks dig hackers. Also, security engineering-type thinking is very compatible with lw-style rationality. It's no coincidence that Wei Dai is a top contributor both here, and in real-world cryptography circles.