What is your goal in sending the newsletter? Do you want to market your site, or your product?
Who will be reading the newsletter? Do you have a list of people who have subscribed from your site? Are they young, old, well to do, rural? Your attitude should depend on this.
What can you say in the newsletter to achieve your goal? How do you connect your readers to your product? (Whether the 'product' is your site or your sale.)
Writing a good newsletter - one that catches the readers attention and appeals to him in some way - isn't a mysterious, difficult thing, but there are a few things to remember as you write.
As designers, we're always looking for inexpensive ways to market our services. Newsletters are a good way - but email newsletters are even better, because they cost nothing except your time.
Can you get more work by sending out an email newsletter? Yes, if you provide content your customers are looking for. Remember, the name of the game in marketing is to keep your company name in front of your customer.