I just went through the Emacs tutorial (C-h t), then used Emacs everyday, for everything. I pick up bits and pieces here and there across the web. I went through Chassel's Emacs lisp book a while back, but can't remember most of it as I felt it's more aimed at developing Emacs itself.

A lot of Emacs is self-documenting and I use that. Look at the docs for the current mode (C-h m), learn keybindings (C-h b), change settings (M-x customize-group), read the info pages (C-h i m emacs).

Funnily enough, studying Common Lisp has helped me more easily read elisp.