I read a page at a time, looking up and writing all unknown vocabulary in a notebook. There could be dozens of new words on the page. I then reread the same page. Usually I can read the entire page through quickly the second time, because it's fresh in my memory. However, when the same words come up again later I may have forgotten the reading or meaning, so it gets another entry in the notebook (even if I recognize it). After noting the same word a few times, I may start to remember it.
The advantage of reading books, in my opinion, is that they tend to use the same vocabulary over and over. You'll eventually remember the most frequently used words naturally. The other advantage is that vocabulary appears in context. This is better for both remembering and for understanding. This is why I don't use flashcards, and just let the book be my study tool.
It's much easier to use this method if the book is selected carefully. It should be relatively easy, but still interesting. Something that might be assigned reading in middle school or high school, I feel, are often good examples.