Indenting and Line Length

Use an indent of 4 spaces, with no tabs. This helps to avoid problems with diffs, patches, CVS 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 php-mode-hook ()
  (setq tab-width 4
        c-basic-offset 4
        c-hanging-comment-ender-p nil
        indent-tabs-mode
  (not
    (and (string-match "/\\(PEAR\\|pear\\)/" (buffer-file-name))
      (string-match "\.php$" (buffer-file-name))))))

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.