Of the various weaknesses I have, flash photography is one of the greatest. Portrait, interior architecture, and so forth.
So, knowing that the Nikon manuals are legendary for their cryptography (I've read them), and my very limited time, I signed up for the CLS class in my area. My particular class was taught by Mike Hagen.
It was great - I only wish that I had sufficient time to practice in the interim, but I did take copious notes, and Mike provided his own PowerPoint slides as well, which have been most helpful.
Quite honestly, there's nothing like a small class with an engaging instructor and hands-on scenarios. Balanced, fill, diffusion, bounced, CLS, stroboscopic, rear sync, and so on. While many of the activities involved portraiture (we were our own willing subjects), they were applicable to all sorts of photography. It was easy to see how the same concepts would apply to studio, macro, and even harsh, midday outdoor conditions.