How to set Auto Fill Mode by default

If you want Emacs to be in Auto Fill mode every time you use it, then you need to put the following lines into a file named ~/.emacs:

(setq default-major-mode 'text-mode)
(setq text-mode-hook
      '(lambda nil
	 (setq fill-column 72)
	 (auto-fill-mode 1)))

The first line makes Text Mode the default for all files without another defined mode (such as C Mode). (You can leave that line out if you wish.) The other lines make Auto Fill mode the default for all Text Mode buffers, and make the lines break at the 72nd column.