1. download the most recent version of virtualbox and install it. (from official website https://www.virtualbox.org/wiki/Downloads
2. download the virtualbox image you want your image to be from osboxes. http://www.osboxes.org/
3. Create a new virtualbox from oracle virtualbox software and then select the downloaded virtualbox image after specifying the memory size for your virtual box.
4. start up the this virtualbox, however you will notice that the screen resolution is not ideal. Enable the first 3 options on Xdiagnose. Restart.
5. install guest additions. using sudo apt-get install virtualbox-guest-x11
you are all set now! Enjoy your ubuntu virtualbox!