Performance optimization is a key element of every website development and often is not considered in the process of designing and theming. We have put together several tips which can help you to improve your site's performance from the Drupal's front-end perspective. I hope you will find these tips useful.

Source: http://developer.yahoo.com/yslow
Use YSlow to identify problems
As on most of our projects we use YSlow as a tool for front-end performance testing and optimization. It helps us to identify problems and suggest a way to improve performance based on the set of rules for high performance websites.