It's ideal where you think you'll find the answer to the question you formed. Usually swiftly over a series of pages till you find your answer then you might find yourself moving to a different section of the book to answer the next question.
If nothing intuitively catches your eyes rephrase your question. You may be looking for a specific way of answering the question though it may be explained more broadly than your question allows for. If you're asking "how" and not finding any answers try asking "why or when?". Remember the answer is usually hinted to with information from headings, subheadings, content and index pages.
Alex
