Steve Souders and the guys at the Yahoo performance group have done a wonderful job at summarizing and explaining where the performance lies for a web page. Of course, summarizing in 13 rules doesn't fit everyone's web site.
Both as a developer, a cto and a project manager, I have come across slow web sites. Some of my worst memories are france2 home page or aol classifieds. But my worst memory of all is the 25th october 2006, when the home of Sfr changed. Since that day, with the help of wonderful people and despite real shmucks, I have learned the hard way 10 rules for performance.
- Redirections are evil
- Trust the cache, and give it as much as you can
- Compress text content
- Watch cookies
- Don't destroy a good first impression with slow https
- Use several sub domains
- Watch your doctype and your syntax
- Reduce the number of http requests
- Make web applications faster
These rules (except number 10) are based on the fact that 80 or 90% of the time to display a page is on the client side. I have learned this during my days as an Html developer (I've done them all), and it's taken me a lot of time to explain it to those wap weenies you find at telcos.
I have written an ebook in french detailing those rules and describing how you can help your pages. I might translate it in english.