A friend of mine took a reading and speed reading class. What this teaches one to do is to skim and look for the important pertinent stuff. I have problems with reading more than ten pages at a time in demanding new works. I do ok when I do such and do not get overwhelmed. That is all it takes.
Some people are just naturally prolific readers.
I am not. Each thing I read makes me think of other things such that I often drift off to something not relevant. It is a matter of practise and developing discipline. As a species we did not develop spoken language over night and we did not develop written language over night we had to study it. I am of the opinion that not always is it the fault of the reader alone but possibly a combination of the writer and the reader of the written material.