Throughout the blogosphere I'm always seeing these blogs, that while they look great, are horribly slow and overburdened. Over the past few months I have become somewhat of a website optimization specialist, bringing my own site from an over 250kB homepage to its current 34kB. I will help you achieve some of the same success with a few, powerful tips. Most of these are common sense, but I can't stress their importance enough. I will concentrate on the website and not the server in this article, as there are too many things to discuss when it comes to server optimization.
1) Reduce Overall Latency by Reducing HTTP Requests
Every HTTP request, or loading each item on your website, has an average round-trip latency of 0.2 seconds. So if your site is loading 20 items, regardless of whether they are stylesheets, images or scripts, that equates to 4 seconds in latency alone (on your average broadband connection). If you have a portion on your site with many images within it, such as your footer, you can reduce the number of HTTP requests with image maps. I discussed that in more depth at the end of this article. If you are using K2, you can get rid on one extra HTTP request by using one stylesheet, style.css, and no schemes (integrate what was in your scheme in the main stylesheet).
Don't Rely on Other Sites!
If you have several components on your site loading from other websites, they are slowing you down. A bunch of HTTP requests from the same server is bad enough, but having HTTP requests from different servers has increased latency and can be critical to your site's loading time if their server is down. For example, when the Yahoo! ads server was acting weird one day my site seemingly hesitated to load as it waited on the Yahoo! server before loading the rest of my content. Hence, I don't run Yahoo! ads anymore. I don't trust anyone else's server and neither should you. The only thing on this site served on another is the FeedBurner counter.
2) Properly Save Your Images
One huge mistake people do is save their image in Photoshop the regular way. Photoshop has a "save for web" feature for a reason, use it. But that's not enough. You must experiment with different settings and file formats. I've found that my header/footers fare well as either PNGs or GIFs. One major contributor to image size is the palette or number of colors used in the image. Gradients are pure evil when it comes to image size. Just changing the way my header text was formatted and replacing the gradient with a color overlay (or just reducing the opacity of the gradient) saved a few kilobytes. However, if you must keep your gradient you can experiment with the websnap feature which removes similar colors from the palette. But if you get carried away, it can make your image look horrible. Spend sometime in Photoshop, saving image for web with different settings. Once you have honed this skill, you can shave off many kilobytes throughout your site. Also, if you use the FeedBurner counter chicklet you can save roughly 2.1kB by opting to use the non-animated, static version.
3) Compression
Along with reducing HTTP requests comes decreasing the size of each request. We covered this case when it comes to images, but what about other aspects of the site? You can save a good deal of space by compressing the CSS, JS and PHP used on your site. Ordinarily compressing PHP wouldn't do anything since it's a server-side scripting language, but when it's used to structure your site or blog, as it commonly is, compressing the PHP in the form of removing all whitespace can help out. If you run WordPress, you can save 20kB or more by enabling WP Admin » Options » Reading » WordPress should compress articles (gzip) if browsers ask for them. Keep in mind, however, that if you receive mass traffic one day you might want to disable that setting if your webhost gets easily ruffled with high CPU usage.
The problem with compressing any of your files is that it makes editing them a pain. That's why I try to keep two versions of the same file, a compressed version and an uncompressed version. As for PHP compression, I generally go through the files by hand and remove any whitespace. When it comes to CSS, I usually do the same thing but have found CSS Tweak to be helpful when dealing with larger files. But do keep in mind that if you compress your main style.css for WordPress with default CSS Tweak settings, it will remove the comments at the top that setup the theme. Be sure to add that piece back after you've compressed it or WordPress won't recognize your theme. When it comes to compressing JavaScript, this site has you covered. However, use the "crunch" feature as I've received weird results using "compress."
Alternatively, you can check out my method of CSS compression utilizing PHP.
4) Avoid JavaScript Where Possible
In addition to adding HTTP requests and size to the site, the execution of the JavaScript (depends on what it does) can slow your site. Things like Live Search, Live Comments, Live Archives are tied to large JS files that like to keep your readers' browsers busy. The less the better.
5) Strip Extraneous PHP/MySQL Calls
This step is probably only worth pursuing once you have completely exhausted the other tips. The K2 theme my site is vaguely based upon originally comes with support for many plugins and features, many of which I don't use. By going through each file and removing the PHP calls for plugins I'm not using or features I don't need, I can take some of the load off of the server. When it comes time to hit the frontpage of Digg or Slashdot, your server will more than thank you. Some aspects of this can be exemplified by hardcoding items where feasible. Things in code that don't change in your installation such as the name of your blog or your feed or stylesheet location, can be hardcoded. In K2 these items rely on a WordPress PHP tag such as bloginfo. It's hard to explain what sorts of things you can strip from your website's PHP framework, but be on the lookout for things you don't use on your site. For example, in the K2 comments file there is a PHP if else that looks to see if live comments are enabled and utilize them if so. Since I don't use live comments, I can completely remove the if part and write it so that regular comments are always used.
Also, using too many WordPress plugins can be a bad thing, especially if those plugins are dependent on many MySQL commands which generally take much, much longer to execute than PHP and can slow a whole page down.
Miscellaneous Thoughts
Even if you don't call on a piece of CSS that has an image, it is still loaded - so you might want to rethink using that one CSS selector that hardly gets called. When it comes to using a pre-made theme for your CMS, it's a good idea to go through the CSS and look for things that aren't used. For example, with K2 there was a bit of CSS defined for styling sub-pages. I don't have any sub-pages so I removed that piece of CSS.
If your site is maintained using a CMS of some sort, you likely have several plugins, if not dozens, running behind the scenes. Going along with the theme of things, you will want to deactivate any plugins that aren't mission critical. They use server resources and add to the PHP processing load.