Emacs frequently has more than one window open, and C-x o can be used to switch between them. C-x o is far less useful when you have three or more windows open, since you need to use it multiple times to reach the desired window. The Ace-Window package improves this situation by allowing you to navigate directly to a window.

(use-package ace-window
  :ensure t
  :pin elpa
  ("M-o" . ace-window)
  (setq aw-keys '(?e ?t ?u ?h ?o ?n ?i ?d)))

I've bound the keys for different windows based on the Dvorak keyboard layout that I use with my Kinesis Advantage keyboard, prioritizing the strongest fingers. The effect of this package can be seen below: