In penance for cracking stupid jokes on Twitter, here's my Emacs cheat sheet. Emacs has a steep learning curve, so I've tried to order them by importance so you could learn them in stages.
One overall rule of thumb: pay attention to the minibuffer (the line at the bottom of the editor). It will often guide you through a process, and also gives you hints about what state you're in, such as the middle of a multi-chord sequence.
The other rule of thumb: when in doubt, C-g it out.
You simply can't get by without having these at your fingertips.