I personally never thought much of the guys giving the speedreading workshops, they seemed to be acting and came across like secondhand car dealers. Their claims of comprehension with over 1500 words / minute just sound insane. The techniques however are not all nonsense, and I do believe that I have learned to increase my reading speed from +/- 300 to around 500 words per minute.
The most important lesson they thought was 'guiding your eyes'. Our eyes are not that good in following a straight line by themselves, just try to stare straightforward, and make a perfect circle with your eyes: it will more likely be a pentagon or something. When we let our eyes follow our finger drawing a circle however, it is a lot easier. Applying this to reading, simply means using your finger or pen to follow each sentence on the paper. I find it a lot faster to read that way, but I still let myself subvocalize the sentences, for comprehension. Doing this on a 500-600 words/minute rate is a lot more exhausting though, and I only use it for academic articles or textbooks.