In Emacs, how do I select the completion list with the keyboard?

In Emacs, how do I select the completion list with the keyboard?

When I tab-complete in a minibuffer and Emacs displays a completion list
in a new buffer, how do I switch to that buffer without using the mouse?
I tried C-x o, but that just switched to the first buffer, out of which I
entered the minibuffer.
I also tried C-x b, but that gives me command attempted to use minibuffer
while in minibuffer.
Lastly I tried C-x <C-right>, which gives me cannot switch buffers in
minibuffer window.