Here are the plugs for your car, click on the "see all" button for other options: http://www.autopartswarehouse.com/details/QQFordQQFocusQQAccelQQSpark_PlugQQ20002008QQA35260SS.html?apwcid=P1135867996W43b3f85c7ab9e&apwid25rLwAK
Go to Auto Zone for a free computer read out and any other parts you need they will tell you about. Review this site on what to do: http://www.automotix.net/autorepair/diy/2008-ford-focus-specifications.html