There are two major factors when it comes to reading. The first is prediction based on your vocabulary, and actual ability to analyze words quickly enough to read them. Reading is linked to speech or vice versa, and being able to talk quickly (expression of thoughts) has an affect on reading. To read fast, you must practice. That is the only real way of being able to improve speed. Generally speaking, you "say" words in your head when you read, so you must be able to pronounce the words you read and be able to understand them quickly. The only way to do this is, as mentioned, by reading more.