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As they say...better to be lucky than good.
I took speed reading in high school, the teacher was also one of our English and Lit instructors, she could read pretty fast. Not like that fat guy on the infomercials, but she could read like 1600 words per minute with high comprehension. There are a few different accepted methods, all of which are labor intensive meaning they require a LOT of reading and practice.
You start out by finding your current reading rates in different situational reading speeds so you will have a basis of comparison. We all change our reading speed based on the amount of time we have to read the material and how much of that material we need (or want) to learn and remember.
Generally, there are three rates. Your 'study' rate where you are trying to get full comprehension (textbooks and stuff). There is a rate for 'pleasure reading' when reading things like novels or magazines. Then there is a 'quick' or 'scan' rate that you use to get at the crux or nugget of what the material is about, such as a newspaper article that you quickly read over.
You take your reading material and figure-out how many words there are on an average page, then you read for several minutes at each of the three rates and find the average words per minute for each rate. It is important that you don't attempt to bias this result or make it look as though you read faster than you truly would in a real situation.
Also, it is of critical importance that you do not select reading material that is unusually complex or difficult to understand. I don't know about you, but I sometimes read stuff that I have to re-read once or twice, then ponder it for a while, before I "get it". That's not the sort of material you want to be using for practice. In fact, no speed reading method will significantly increase the rate at which you can "take in" unusually complex or difficult material because your rate of reading isn't the issue here. The 'bottleneck' is elsewhere.
The goal is to increase each of the three rates without losing their respective comprehension levels. This is done gradually. As I said, there are a few different accepted speed reading methods, so I won't go into each of them, except to say it is well known that not everyone will respond as well to the same method. People who don't benefit much from one method might benefit more from another, etc.
The results in my class were that everyone at least doubled their rates without loss of comprehension, a few tripled their rates and a few others quadrupled. Nobody became a "superhuman reading machine" like you read about. I remember my instructor saying that in the 15 years she had taught the course, only one student could surpass her abilities but not by much and the "superhuman reading machine" is an unattainable goal for about 99.7% of the population.
But, it is a skill that you develop and like any skill, if you don't regularly USE it, you'll lose it, which is what happened to me. ;-)