Maggie Toussaint wrote a great, simple little article on what to include in your newsletter over at The Wild Rose Press blog. Check out an excerpt:
You need to mention right up front the most important thing – whether its a new contract, a contest, a new release, or a booksigning. Make sure people know how to buy the book! You need to let everyone know where to find you – your appearances in person and online. You should have something tantalizing about the story or about how you write.