I have read a couple of books but the one that I think is important is titled "No: Why Kids of all ages need to hear it and ways parents can say it" written by David Walsh. The book covers a lot of really good points. A description of the book I copy here from Amazon....
From Publishers Weekly
Psychologist Walsh (Why Do They Act That Way?), president and founder of the National Institute on Media and the Family, tackles a tough subject in this book on how parents can say "no" to their kids and why they should. Walsh argues that we are raising our children in a "Yes" culture that gives kids the message that they can and should have whatever they want whenever they want it. But scientific research, the author contends, reveals that children's brains are primed to learn the concept of "no" early on; in fact, Walsh points out, instant gratification is not the path to resiliency or success. On the contrary, our "yes" culture leads to disappointment and failure when kids later learn that they can't always have their way. Walsh's approach fosters such qualities as perseverance, patience and commitment, emphasizing a balanced parenting style that is neither predominantly negative nor permissive. In age-by-age chapters, he chronicles the developmentally appropriate use of the word, revealing how it helps children grow into self-disciplined, well-adjusted adults. Peppered with anecdotes of other parents' struggles as well as examples from raising his own three kids, Walsh's reassuring voice will give parents the courage to just say "No"—and mean it. (Jan.)
Check out the book...you can probably get a pretty cheap copy on Amazon.