Indenting and Line Length

Use an indent of 4 spaces, with no tabs. This helps to avoid problems with diffs, patches, SVN history and annotations.

For Emacs you should set indent-tabs-mode to nil. Here is an example mode hook that will set up Emacs (ensure that it is called when you are editing PHP files):

(defun pear/php-mode-init()
  "Set some buffer-local variables."
  (setq case-fold-search t)
  (c-set-offset 'arglist-intro '+)
  (c-set-offset 'arglist-close '0)
)
(add-hook 'php-mode-hook 'pear/php-mode-init)

Here are Vim rules for the same thing:

set expandtab
set shiftwidth=4
set softtabstop=4
set tabstop=4

It is recommended to keep lines at approximately 75-85 characters long for better code readability. Paul M. Jones has some thoughts about that limit.