Then the Internet happened and the rules were changed. In 2001 Zona Research released report that stated that the average web user will wait about eight seconds for a page to download, later known as the ’8 second rule’.

For a long time, by Internet standards, the 8 second rule misguided web workers to create web pages that just barely keeps the user focused. If you already haven’t it’s really the time to create a web page that get your users to feel they are interacting freely. Its time to create a web page that loads up at a lot close to 1 second than 8.

Dust-Me Selectors a Firefox extension

Dust-Me Selectors is a Firefox extension that finds unused CSS selectors. You can test pages individually, or spider an entire site, and you’ll end up with a profile of which selectors are not used anywhere. Essentially it removes unnecessary data that is transferred to the user.
Download Dust-Me Selectors from Sitepoint

WP CSS a WordPress plugin

<link rel="stylesheet" href="/wp-css-compress.php?f=style.css" type="text/css" />

This plugin will combine all your stylesheets in to one, thus reduce the number of HTTP requests required to render the page. It will also strip your files from whitespaces, compress it with GZIP and set a cache expiry time of your choosing.
Download WP CSS from WordPress

WP JS a WordPress plugin

<script src="wp-js-compress.php?f=1.js,2.js,3.js" type="text/javascript"></script>

This plugin will GZIP and JSMIN your JavaScript files as well as allowing the ability to put JavaScript files into a single file at the client’s end. Just like the WP CSS plugin this will reduce the number of HTTP requests and lower your blogs response time.
Download WP JS from WordPress

WP Super Cache a WordPress plugin

This plugin generates static html files from your dynamic WordPress blog. After a html file is generated your webserver will serve that file instead of processing the comparatively heavier and more expensive WordPress PHP scripts. Super Cache also has the feature to compress your html files using GZIP. There is also a special version of WP Super Cache which has the ability to minify HTML.
Download WP Super Cache from WordPress
Download WP Super Cache with WPSCMin from Lyncd

Optimize DB a WordPress plugin

This plugin lets you optimize the tables of your database, to reduce their overhead.
Download Optimize DB from WordPress

Yahoo YSlow a Firefox Firebug extension

YSlow analyzes web pages and suggests ways to improve their performance based on a set of rules for high performance web pages. It lets you know if you have too many DOM elements, if your javascripts are positioned wrong, if you compression is working and much, much more.
Download YSlow from Yahoo

Last, but not least. Upgrade and do a clean up.

Upgrade WordPress to the latest version. Remove the plugins you are not using and upgrade those you are. Keep your code light. Try to code what you want to code with as few words as elements, attributes and functions as possible. Minimize requests, use css sprites and read Yahoos guide about ‘Best Practices for Speeding Up Your Web Site’.

One way of reducing the number of HTTP requests while still support rich page designs is to use a server side script that combines all your javascripts and styles into single files. A php script that does exactly that is Rakaz’s combine.php.

When the script is configured and ready to use all you need to change are the urls to your scripts and styles. You will go from doing, in this case, four requests to only one.

	
	<script src="jquery-1.3.2.js" type="text/javascript"></script>
	<script src="jquery.valid8-1.1.1.js" type="text/javascript"></script>
	<script src="jquery.defaultvalue-1.0.js" type="text/javascript"></script>
	<script src="global.js" type="text/javascript"></script>

	
	<script src="jquery-1.3.2.js,jquery.valid8-1.1.1.js,jquery.defaultvalue-1.0.js,global.js" type="text/javascript">

Rakaz’s script will also compress and cache your combined files to reduce loading times even more. You can find a complete installation guide and more information about the script over at rakaz.nl

Real world example

I just uploaded and configured combine.php for http://chat.unwrongest.com. Before the script was added you needed to download 10 javascript files that weighed 232 kb in total. On average this took about 3 seconds to download. After installing the combine.php script you now need to download only a single file of 68 kb which only takes around 1 second to download. The total loading time of chat.unwrongest.com is now, for me, around 2 seconds instead of just above 4 seconds.