Update 2015-05-04: Note that much of the advice here will become outdated with HTTP 2, where there should be little to no performance degradation when serving many smaller files, and where compression might be on by default!
Web development today is a constantly struggle between three major stakeholders: the customer, the designer and the developer. The customer tries to push through his or her (often distorted and silly) mental image of the website, the designer wants to be original, creative and fancy creating lots of intricate designs with fancy visual effects, and the developer who attempts desperately to explain to both the customer and the designer why what they’re doing is a bad idea (heavy background images, crammed pages, no whitespace, confusing visual effects…). The developers aren’t all good either though - They tend to put in as many fancy tricks and solutions in the final product as they can, often resulting in exotic bugs in various browsers and usually ungraceful downgrading™. In all of this, one stakeholder is often wholly forgotten, even though it is probably the most important one; the users.
Users often don’t know the first thing about how the web works. They don’t care whether the site is optimized for Firefox, Internet Explorer, Chrome or Safari (in fact, they probably don’t even know what a browser is) The users want a site that is visually appealing, but not distracting - informative, but not cluttered - clear, but not over-simplified - and most importantly, one that is responsive. When a user does something, they should begin to see something happening within .1 seconds to feel as though they aren’t being slowed down by the site itself. Furthermore, the total loading time for whatever action the user initiates should be less than a second for the user not to fall out of his or her “flow”. Way to many websites violate these simple rules, causing the site to feel unresponsive to the user, and the users are likely to jump to the next site on their list.
In this post, I hope to show you how to make your website faster - mainly through optimizing the initial page load. In order to do this, there are three steps that need to be taken: Combine, Compress and Communicate. Repeat after me: Combine, Compress and Communicate.
All your images should be done as sprites. Ideally, you should even be able to put every single image on your site into a single png image. Do this, and you will substantially reduce the loading time of your site. For an introduction to CSS sprites, have a look here.
Apart from minimizing the files, you should also compress them using something like GZip which is natively supported by several browsers. To see how to do this automatically with Apache2, have a look at this guide.
First of all, you need to tell your web server to send out as much data as possible about your file. This especially applies to dynamic files such as those created by PHP. Have a look here for a more thorough discussion of this topic.
Second, files that are GZipped by Apache don’t always get an expiration date, causing the browser to re-download the file on every page load. To overcome this problem, have a look at the first answer on this page
In the course of this post, I hope I have given you an overview of what can be done to speed up the loading time of web pages, and enough pointers to keep you going in your quest for the best speed your website can achieve. This is an ever-expanding topic, and new techniques are always appearing, so you should attempt as best you can to keep up to speed (pun intended) on the newest advances in the field.