1. The Last Dive - great read, lots of background/history and general information on technical diving.
2. The Oxygen Hacker's Companion - THE source regarding gases, mixing, and other essential knowledge for the person making the jump into tech.
3. Stuff on the Internet - you can read it here, elsewhere, or some of it in "Doing it Right: The Fundamentals of Better Diving", by Jarrod Jablonski. Regardless, moving into the technical realm will require refinements in technique and skills that can be read about in some of these sources.
4. Go diving...a lot...preferably with someone that is doing the type of diving you aspire to be doing yourself.