If your author is a good author, he or she will begin each paragraph with a key statement that tells you what that paragraph is about. By reading only the first sentence, you can determine if the paragraph has information you need to know.
If you're reading literature, this still applies, but know that you may miss details that enrichthe story. When the language in literature is artful, I would choose to read every word.
The last sentence in a paragraph should also contain clues for you about the importance of the material covered. A last sentence often serves two functions -- it wraps up the thought expressed and provides a connection to the next paragraph.
When you've skimmedfirst and last sentences and determined the paragraph is worth reading, you still don't need to read every word. Move your eyes quickly over each line and look for phrases and key words. Your mind will automaticallyfill in the words between.