Figure out what your clients need most for tips (organization, time management, marketing...) Then you create an article that will help them. Then you create your focus area or special that you offer that will help them out if they hire you.
Remember that you can only email people that you have had some form of contact with in the past.
MailChimp is a free email marketing site that allows you to have 500 contacts and send 3000 emails a month. You can join at
http://www.mailchimp.com With MailChimp you can also hook up a sign-up form for your website to request your newsletters.
I originally created my newsletter on Publisher and found that I was not able to use it on MailChimp so I transformed it into a flyer to fax to potential clients. Attached you can find that newsletter to give you an idea of what you could do.