In my opinion practice is the best teacher when it comes to reading speed. The more words you know, and the more you get used to them, the less time your brain will need to recognize them and distinguish them as those specific words, therefore you can move on to the next word faster. There are some books especially adapted for language-learners and they have their difficulty level marked on the back. I suggest buying one and then progressing onto the next level, might be a good start.