The biggest thing about learning how to use Emacs is ... (drumroll please) learning how to use Emacs.
Okay, okay, okay. It's a silly answer, and it's a tautology, but it's true. If you start up Emacs, and think to yourself "How could I find every instance of the word 'foobar' in my source tree?" the worst thing you could do is hit Alt + Tab and visit Google.
Learning the help system and how it works is the best thing you can do. It's so nice to just hit C-h a find, and suddenly get all the information you need, right at your fingertips.
The next best thing you could do is install a wonderful little package called Icicles which has some seriously groovy completion functions. After you get it installed, just know that anytime the minibuffer is asking for some kind of input, you can now use regular expressions.
How would this apply to finding every file in your source tree? Well, you'd hit M-x, and then type "find". After that, you could hit (for instance) Shift + Tab and Icicles would kick in, finding every command that prefixes with "find". Alternatively, you could do M-x .find. and it would give you any command with find in it.
Build a cheat sheet. Just keep a saved buffer somewhere that has all of the keyboard shortcuts you use frequently in it. Remove the ones that you know off by heart, and pick up new ones. In most cases when you do a M-x command, the message buffer will tell you what the keyboard shortcut was for that command (if there was one).
Steven Huwig's idea of using some killer applications is a good one. Emacs is easier to use when you want to use it. For me, it was Planner Mode. (I've just moved to Org-mode, and it's even better.)
+1, but C-h c maps to describe-key, which isn't what you meant I don't think when you said "C-h c find". "C-h a find" maybe?
Good advice (learning the help system, creating a cheatsheet - in emacs!) +1.
See, in particular, this page about using Icicles to help you learn Emacs: EmacsNewbieWithIcicles.