Cleaning up all those unnecessary junk files

1) Tip #1 - Getting rid of Residual Config packages
Residual Config packages are usually dependency packages that are
left behind after you uninstall a package from your machine. To use this
feature, go to System > Administration > Synaptic Package Manager.
On the bottom left hand corner of the window, click the Status button.
In the list above the Sections, Status, Search, and Custom buttons, Click
on the "Residual config" text. To get rid of these pests, click on the
box to the left of the package name and select "Mark for Complete Removal".
After you have done that for all of the Residual Config packages, click
"Apply".
2) Tip #2 - Getting rid of partial packages
in the Terminal, key in the following command:
sudo apt-get autoclean
3) Tip #3 - Getting rid of "orphaned" packages
Download the "deborphan" package found in Synaptic Package Manager. Then:
sudo deborphan | xargs sudo apt-get -y remove --purge