Allthough I bring their feed, I have to put this article from Debian-Administration up here – it begins “You arrive at a Debian GNU/Linux server which has some history of neglection.”
Read the rest of the story and tips here
Let's suppose someone else neglected it but if your new-year resolution is to stop neglecting your beloved server, this applies as well.
One form of neglection is to install, install, install and never un-install any package. The common utility to perform installation and un-installation of packages is apt-get which adds to the problem because it doesn't have automatic removal of non-needed dependences.