Go directly to the Executive check-in desk (through the blue doors, to the far right). As a Diamond, you will get access to the excellent Executive lounge. You should get an upgrade to one of the executive floors higher up as well.

Also see these threads (among many others):

http://www.flyertalk.com/pasttalk/ft...ML/001554.html

http://www.flyertalk.com/pasttalk/ft...ML/000618.html

http://www.flyertalk.com/pasttalk/ft...ML/001026.html