Try these in your .emacs:

  (setq whitespace-style '(tabs trailing))
  (add-hook 'lisp-mode-hook 'whitespace-mode)

  (defun untabify-buffer ()
    (untabify (point-min) (point-max)))

  (add-hook 'write-file-hooks 'untabify-buffer)
  (add-hook 'write-file-hooks 'delete-trailing-whitespace)