If you want to get good publicity out of letters to the editor you need to be aware of how frequently to send the something.

If you're throwing out something every month where it looks like you're almost desperately trying to find something to connect with, editors aren't going to like that, because they're going to tell that this woman's just trying to sell her book, and you don't want that. I think it's very much in terms of the feel of the letter and I think Joan is very much on target about not even mentioning the book. The letter has got to come off as looking like you were struck so much by a particular issue that you wrote a letter. If you want to pull from the book some of the messages and ideas that you have, and as she said, writing "as I've written." or "as I wrote." or something, and then follow that up later on, that's a much better tack because as soon as it gets that sort of scent that "I'm selling something," you're out the door.

You can find more great information like this in How to Use Newspaper and Magazine Editorial Pages.