These aren't hard-and-fast rules or formulas but they are tried-and-true guidelines that hold true most of the time.
Quickly Checking a Book
A good way to get the "feel" of a book is to read the table of contents, then read the index, if it has one, and finally read the first and last paragraphs of each chapter.
Looking Over a Computer Manual
If a manual's table of contents lists names of programs or components instead of tasks, the manual isn't "user friendly."
Size Matters
Bigger isn't necessarily better. If you feel intimidated by the size of a book, you'll probably not read it. Start with smaller, more basic books to become familiar with a concept. Later, you can learn the nitty-gritty details and more technical aspects found in larger, more comprehensive manuals.