If you're a bit new, then Bleachbit is another excellent cross-platform (yep, you can use it in both GNU/Linux and MS Windows) free utility, that lets us remove unnecessary files (such as cache and other temporary settings) of a lot of individual applications from a singe "command center" window :).
It cleans the web browser cache, cookies, history (Firefox, Safari, Chrome, Chromium and a whole lot others!), GIMP, OpenOffice (although LibreOffice ain't supported yet), MS Office, Gnome 2 and the Gnome 3/Shell desktops search and history, Skype, TeamViewer, Yum (Fedora's default software manager), Wordpad, Winrar, Winzip + a huge list of other apps as usual.
|"one place to rule them all!" ;-)...|
New features in the 0.9 version...
*. Bug fix related to Thunderbird 5 in GNU/Linux.
*. Removes recently used files entry in Gnome 3.
*. Wallpaper erasing bug (errrr) fixed under Gnome 3.
*. GNU/Linux Kernel 3 support... are among the main ones considering the GNU/Linux users.
|You can click on that "Preview" icon anytime to see a preview cleaning which displays things like how much space you'll be recovered, which settings are gonna be cleaned, etc ...|
Then after the installation completes, just double click on it and follow the on-screen instructions. That should do it. So as a final note, if you're looking for a comprehensive system cleaner for Ubuntu ... then BleachBit is one of the best without a doubt!.