Following are the few Tips to optimize and to increase the speed/performance of Drupal based website:
1. Uninstall unneeded modules.
2. Remove unnecessary content.
3. In admin/settings/performance change the Caching Mode to Normal.
4. In admin/settings/performance change “Aggregate and compress CSS files” to Enabled.
5. Install a PHP Accelerator (i.e. eaccelerator, xcache, etc).
6. Analyze database queries. Create indexes for your Drupal database if required. And look for slow queries.
7. Install and configure memcached. Memcached Details can be found here: http://drupal.org/project/memcache
8. Install advanced cache module.
9. Install and Configure QueryCache module. Details can be found here: http://drupal.org/project/querycache
10. Set HTTP headers cache options to optimal values.