Via M-x all-things-emacs, an Emacs feature I've always wanted and has been there all along: navigating between windows using cursor keys.
(windmove-default-keybindings)
Shift + a cursor key moves to the window in that direction from the current window. You can change the modifier from Shift with an argument to this function:
(windmove-default-keybindings 'meta)
Or you can pick your own key bindings for the windmove-* functions, where * is up, down, left or right.
I am never typing C-x o again.