We've seen examples of mistakes you can make that will cause your WordPress-powered site run worse... but how about some advice to make it run better? There are a number of simple tweaks you can make, sure, but there's one thing that will often trump any other improvement -- disabling slow plug-ins.
Marcus Taylor over at Smashing Magazine has put together a comprehensive article covering a variety of ways to speed up WordPress. The obvious tips include using a caching plug-in, enabling gzip compression and minifying your style sheets and scripts, but there are two in particular that caught my eye.
First-off, if you need reliability and performance, nothing is going to have as much impact as selecting a quality host. Shared servers can certainly provide a cheaper option, but if your site is constantly going down, taking seconds to deliver pages or giving you limited functionality (in terms of PHP versions, opcode caching, etc), then it might be time to spend the extra coin and get a chunk of hardware to yourself.
Secondly, Taylor mentions a nifty plug-in called "P3" that will let you quickly identify plug-ins that are crippling your site's performance. True, you could use a process of elimination to figure out the culprit, but it's extremely convenient not to have to disable functionality or go through the trouble of checking your plug-ins in isolation.
If you do check out the article, I'd recommend browsing the comments. Like a number of other readers, I'm not an advocate of using CSS sprites. It does make updating a site or changing the design more time-consuming for an arguably small gain.
How To Speed Up Your WordPress Website [Smashing Magazine]