If you use any given tool for a long enough period of time you will find problems with it no matter how perfectly crafted it might be. WordPress is a tool like this that does a spectacular job of managing content as a barebones application but when you start modifying it to suit your own unique needs it can also impact the performance of it whether it really slows down or just seems like it has. Here are some basic tips and troubleshooting steps if it seems like your installation has started exhibiting signs of sub-par performance.
1. Plugins are often a source of grief for WordPress users as they are developed (usually) outside the framework of the application and, in the case of older plugins, may use features of WordPress that are deprecated and on their way out of use. One of the first steps that you can take to test this out is to disable all plugins via the link at the bottom of the Plugin page in the administration area and then reactivate each of them one at a time until you can isolate the one exhibiting problematic behavior. Usually this examination will yield a plugin that is badly outdated. Find the newer version of the plugin and try it out. In most cases, this will solve the problem but if the behavior persists then report the situation to the plugin developer and do a quick search of the WordPress forums to see if other users are experiencing the same problem. The forums can often give you ideas of how to work around the problem.
It can also be helpful to use the plugins that are available from the WordPress Plugins repository as newer versions of WP actually track the versions of plugins and will notify you via the Plugin screen when newer versions are available. Take advantage of this feature whenever it is possible as it will save you valuable time searching around when you experience an issue with a plugin.
2. Consider caching. If your public facing pages are loading slowly you might want to consider the use of a plugin like WP Super Cache to make pages load faster. This plugin won’t help you as a registered user but it will reduce the overall system load by serving up static pages to visitors who don’t leave comments. This will also protect your server from getting crushed should you be linked from a huge aggregation site like Digg or other sites that generated huge amounts of incoming traffic.
3. Examine your logs. Translate that title into “talk to your service provider” if you’re using a hosted site as they may grant you access to your logs or help you identify potential problems that may show up in system logs. There isn’t an easy answer using this suggestion as hosting environments vary wildly but what you’re looking for are repeated errors that happen with regularity and the sources of the error.
4. Look at your database. WordPress relies on a database to store everything so problems with the database or connections to it are another potential source of complications. Unfortunately diagnosing database problems from within WP isn’t possible at the present but most hosted environments will have some access tool that allows you to examine databases. PHPMyAdmin is the most common of these and you can use it to analyze your database tables and repair damaged tables if it is necessary.
5. Look at your situation. If you’re dealing with a lot of traffic and a tiny hosting company or some antiquated hardware of your own that seemed good enough when you started then you need to strongly consider upgrading your hosting solution. Take it as a measure of success that people want to access your site and realistically reassess what you need to continue delivering the same content without crushing your host or your machine.