Best Practices for Speeding Up Your Web Site

1. Minimize HTTP based Requests

2. HTTP Compression

3. Correct Formatted Images at the Right Place

4. Compress CSS, JavaScript and Images

5. CSS at Top and Javascript at bottom

6. Content Delivery Network: (CDN)

7. Ajax vs. Callback

8. Reduce Cookie size

9. Use Cache appropriately

10. Upload compiled code rather than source code

A good article by Adnan Aman Please check below

http://dotnetslackers.com/articles/aspnet/ImproveWebApplicationPerformance.aspx

http://developer.yahoo.com/performance/rules.html