Each type of reading has a different rate; an exciting novel is a quicker read than a text in biology.
Text books vary in how well they are written;as a consequence some are more difficult to read.
Each semester, time yourself reading a chapter in each of your text books. See how many pages an hour you can read. Once you have an accurate estimate of your reading rate, you can better plan your reading time and studying time.
Scan the chapter first.
the sections to which the author devotes the most amount of space. If there are lots of diagrams for a particular concept, then that must also be an important concept. If you're really pressed for time, skip the sections to which the least amount of space is devoted.
Read the first sentence of every paragraph more carefully than the rest of the paragraph.
Take notes on headings and first sentence of each paragraph before reading the chapter itself.
Then close your book and ask yourself what you now know about the subject that you didn't know before you started.
Focus on nouns and main propositions in each sentence. Look for the noun-verb combinations, and focus your learning on these.
For example, consider the following text:
Classical conditioning is learning that takes place when we come to associate two stimuli in the environment. One of these stimuli triggers a reflexive response. The second stimulus is originally neutral with respect to that response, but after it has been paired with the first stimulus, it comes to trigger the response in its own right.
Rather than read every word, you might decode this text graphically:
Classical conditioning = learning = associating two stimuli
1st stimulus triggers a response
2nd stimulus = originally neutral, but paired with 1st --> triggers response.
Rather than reading and re-reading your text, take notes in this form, so that you've re-written the important parts of the text. Once you have written notes, you don't have to worry about the text itself.