Installing VirtualBox Guest Additions

[Colin Law]

HI

I have Installed Ubuntu 11.10 as guest OS in VirtualBox running in
Ubuntu 12.04.  I understand that to get the best performance I should
install the Guest Additions, but am not sure of the correct way to do
this, google having found conflicting advise on this for me.  For
example [1] provides two different methods, one in the text and
another in the first comment, and when I attempted this some time ago
I think I used another method, which I was never quite sure had worked
properly.  What is the recommended way of doing this please?

Colin

[1] http://ubuntu-tutorials.com/2010/06/26/install-virtualbox-guest-additions-on-virtualbox-guests/