Read the original post here. It includes screenshots. Only that post contains some errors, so use my commands instead.
Read this official MATE site for more detailed technical installation tips.
If you like GNOME 2 more than GNOME 3 or Unity, consider installing MATE. It's very like GNOME 2.
MATE isn’t available in Ubuntu’s repositories, but the MATE developers offer an official repository for Ubuntu. Unlike some methods that recommend you use Linux Mint’s repository on Ubuntu, this won’t mess up your system.
Launch a terminal window from the Dash and run the following command to add the MATE repository to your system:
This command works for Ubuntu 11.10, Oneiric Ocelot. If you’re using a different version, replace “oneiric” with the appropriate word – for example, “precise” for Ubuntu 12.04, Precise Pangolin.
NOTE for Linus Mint you don't nbeed to do this as Mint has Mate in its standard repository.
Next, run the following command to download a list of the available packages:
Use this command to install the MATE archive’s key. The archive uses this key to digitally sign its packages:
Finally, run the following command to install the MATE desktop:
Type Y and press Enter when prompted.
You may also want to install the mate-utils package, which contains the screenshot tool and other small utilities. (That’s “sudo apt-get install mate-utils”.)
Log out from the menu at the top right corner of the panel after installing MATE.
Select the MATE desktop from the list on the login screen before supplying your password. It's in the right button next to your name when logging in.