I wanna share solutions that i have adopted to speed up your WordPress blog for what i have read on web.
The benefit, over the most satisfaction of visitors, is also about SEO level, in fact it affect Google ranking.
1. Use a lightweight theme
a light theme (look for minimalistic for example) both for graphic and PHP functions/scripts used inside the theme is the starting point.
As maybe you can notice you see many important blogs use simple and clean themes/templates.
2. Make performance analysis with Firebug (and the addons Pagespeed and Yslow)
Firebug is a useful tool (Firefox addon) mainly used to make code debug, but it is also useful for performance measurement (tab “All” -> subtab “Net”): all the requests and load time are analyzed. For a better analysis you can use Google Page Speed Firefox extension, you can analyze time of web pages and the score obtained, you can then see various alerts and also suggestions for speed otpimization; another similar extension is Yahoo Yslow
3. “minify” style sheets and Javascript scripts
within specific WordPress plugins you can render more small the size of CSS and JS files within a technic that “compress” them.
You can use the specific module on W3 Total Cache plugin (see next point)
4. enable and use caching
within some specific plugins you can enable caching on pages, this means that they will be saved on your web server the first time and served static (so more fast) when they are recalled.
They are various plugins, what i found more performant is W3 Total Cache; the default settings generally goes well, but if you wanna go more in depth you can follow the guides fromZemalf.com and/or StrictlyOnlyBiz
5. use the Apache module mod_pagespeed if your hosting has an option for it
it’s a recent Apache module developed by Google, look this video comparison
6. optimize your database occasionally
it’s a good thing to optimize WordPress database tables, you can directly do from PHPMyAdmin or using specific plugins (eg. WP-Optimize)
7. choose a reliable host
a web hosting service with good bandwidth and that can easily handle multiple connections at same time
8. resize big images and host them in specific services if possible
try to compress much more possible the images of your blog (especially the big ones) and if you can it’s best to host them in specific image hosting services (eg. Picasa, Flickr, etc…) instead your own web server