Once everything works, we want to make it faster to improve the user experience. The first stop should be Yahoo!'s Exceptional Performance team site (http://developer.yahoo.com/performance/) and, in particular, reading their recommendations at: http://developer.yahoo.com/performance/rules.html.
Those recommendations are quite easy to follow thanks to a tool the team has made and is available as an add-on to Firebug. You can actually have it loaded all the time and forget about it. When you want to try it you just click on its tab in the Firebug panel and let it try a page; it will provide you with an overall grade and a detail for each of the categories, with links to the particular entry in the team's site explaining what the problem is and how it can be fixed.
The website for YSlow reports improvements of 25% to 50% in performance. The best part of it is that we can incorporate many of its recommendations as a standard coding practice (for example, <style>...