The overall performance of your database can be greatly improved by tuning a set of most expensive or most often executed queries. In this article, I will look at some of the techniques you can employ to identify and tune the most expensive and worst performing queries on your server.
follow the below link for more detail http://blog.sqlauthority.com/2009/0...imization/
You can also try out some tools mentioned in other thread also which will help you to improve your server performance as well
have a look at this article... http://download.cnet.com/Lepide-SQL...61147.html