One thing I've learned is that Inside Macintosh is just the primer. It may look like all you need - it lists all the Toolbox functions and how they work, and walks you through how things ought to fit together!
But in reality to make anything beyond TeachText you need to read: every Technote, every Q&A, skim every relevant sample code, every Snippet, and also read every issue of develop.
Then you can start to approach being able to attempt to do something!
An example of how you really need to read everything to know how to do anything
1. Inside Macintosh: Networking (my Bible), just says this about completion routines
2. Meanwhile, if I had read IM: Files, I would have learned this convention about using the A0 register (note: never updated to mention PPC) and been referred to IM: Processes. OK so does this apply everywhere or just Files?
3. IM: Processes also doesn't mention A0 params, just gives some helpful hints on working during interrupt
Karl Baron