Note: Gnome-Shell is still in the development stage and there is always the possibility of something breaking.
1. Open terminal and run the command below to install the Gnome Shell
sudo apt-get install gnome-shell
2. After the installaton is done you can start it using the command below in terminal
3. If you have intel graphics and get just a blank screen after the above command run the command given below before the command in step 2.