If you're a slow reader, then reaching 400 words per minute or more might seem like an impossible task. That's not taking into considering reading comprehension -- what good is being fast if you're not absorbing anything? One way to improve your abilities is computer-assisted speed reading, something you can get right now in your browser with a bookmarklet called "Squirt".
To use Squirt, you'll need to add it to your browser as a bookmark -- a tutorial is available if you're not sure what to do. Once installed, you can browse to a page you'd like to speed read and either click the bookmark or, if you want to take in part of the page, select the appropriate block of text and then use the bookmark.
You'll then be shown one word at a time, with the most significant letter highlighted in red. By focusing on this letter, rather than the entire word, you should be able to interpret what you're reading faster.
The default speed for Squirt is 400 words per minute, but feel free to increase or decrease this, depending on your comfort level.