Don't change anything unless you know you have a problem.

http://sqlinthewild.co.za/index.php/2010/03/11/the-root-of-all-evil/

http://www.simple-talk.com/sql/performance/finding-the-causes-of-poor-performance-in-sql-server,-part-1/

http://www.simple-talk.com/sql/performance/finding-the-causes-of-poor-performance-in-sql-server,-part-2/

First thing you need to do is test the DB and the website under the expected load and see how it behaves. You can but load-testing tools for websites, I don't know names offhand.

Clustering is not for performance. Clustering is a High Availability technique (and is reasonably expensive)