Some following tips are derived from the book High Performance Web Sites (O’Reilly) by Steve Souders:

1. Make fewer HTTP requests to reduce object overhead.
2. Use a content delivery network.
3. Add an Expires header.
4. Gzip/compress text components.
5. Put stylesheets at the top in the head.
6. Put scripts at the bottom of the body.
7. Avoid CSS expressions which are CPU-intensive and can be evaluated frequently.
8. Make JavaScript and CSS files external.
9. Reduce Domain Name System (DNS) lookups to reduce the overhead of DNS delay by splitting lookups between two to four unique hostnames.
10. Minify JavaScript.
11. Avoid redirects which slow performance. It’s better to CNAME or alias.
12. Remove duplicate scripts to eliminate extra HTTP requests in Internet Explorer.
13. Configure ETags for sites hosted on multiple servers. FileETag none in Apache removes Etags to avoid improper cache validation.
14. Make Ajax cacheable and small to avoid unnecessary HTTP requests.