>>18
Knowing Common Lisp helps a lot, but knowing when not to use cl-lib is also good. But when it comes to learning, i think "lazily learning" is the best way, but not only while you're extending your init.el, but also whenever you're curious as to how a functionality is implemented (C-h k with local emacs sources are useful). Reading the entire manual will be of little use, consider skimming it or section from time to time, so that you have an idea of the vocabulary when it need it.