apt¶

To fix any broken packages.¶

apt-get -f install

If your disk is full, this may or may not work depending on whether the broken package has been completely downloaded.

to free up some space¶

aptitude clean

This will clean your apt package cache (these are .deb files for the packages you installed; stored in /var/cache/apt/archives); the actual packages will remain installed, but you will no longer have the .deb files on disk and would need to re-download them if you purge/re-install an existing package.