1) Install Fooman Speedste

http://www.magentocommerce.com/extension/457/fooman-speedster

2) Enable Gzip Compression in .htaccess

Add “php_flag zlib.output_compression on” in .htaccess file

3) Install APC or Xcache or memcached

4) Make sure your Apache configuration has KeepAlives enabled

5) Modify the configuration for your MySQL server to take better advantage of your server’s RAM.

6) Use a memory-based filesystem for Magento’s var directory

7) Clustering

8 ) Optimizing MySQL Database

9) Magento Caching.

10) Remove Home Page Elements

11) Compressing CSS Files

12) Changes to MySQL Configuration

13) Change from Apache to Litespeed Web Servers