My base reading speed for most English-language books and other publications is about 500 words per minute, with good comprehension by test. I have never had any trouble at all finishing all the sections of a standardized test with time to spare, for example, whether the SAT or the GRE or the LSAT. There is a huge published literature on reading skills improvement, for readers of all levels of reading proficiency, and when I was in university I read many books about that topic, including some books that made incredible "speed-reading" claims, to see what I could do to improve my ability to finish my homework while working my way through my university courses. One distillation I have of all the advice I read is that it helps reading speed and comprehension a lot to improve vocabulary. English vocabulary improvement can build on studying common Greek, Latin, and French word roots that show up over and over in English words. Doing that seems to have done the most for my reading speed and comprehension, which was never bad in English. A book I recommend for vocabulary development is English Vocabulary Elements 2nd edition.[1] To bolster my reading speed in other languages, I've also had to focus on reading practice and acquiring reading vocabulary. In Chinese for foreign learners, the materials by the late John DeFrancis, his Chinese Reader series in beginning, intermediate, and advanced levels, are still the best available for that purpose, although they appear to be going out of print.
[1] http://www.amazon.com/English-Vocabulary-Elements-Keith-Denn...