As you install, uninstall and update applications there are some garbage left behind.

Autoremove

When you run autoremove, packages that have been installed but are no longer in use, are removed.

sudo apt-get autoremove 

Autoclean

Autoclean removes .deb files from packages no longer installed on your system.

sudo apt-get autoclean 

Do you have other cleaning tips? Send me an email or post a comment.