#1: The AC3D Manual (comes free with the program)!
Seriously, though: some of the more popular (and expensive) 3D programs, like Max and Maya, have trade press books that can teach you how to use their rather deep and involved features and functions.
Also, in the 3D Max community, there is TONS of data free on the web that will show you how to do a LOT of different types of modeling. These can help you to some degree, although you'll still have to figure out how to translate common concepts to the AC3D interface.
But, I'd say that if you're learning 3D modeling, it's the basic core concepts (the various geometries, editing tools, modeling "strategies", etc.) you need to learn, even as much as learning the particular menus and interfaces. These are not exactly intuitive, but really they're the core of EVERYTHING. Once you learn those basics, you can pretty much make a go of modeling anything.
Also, it helps to learn on similar types of objects that you plan to model. What is your interest?