"We are just starting a newsletter. I would like to send both print and email. How do I know who to send what first?"
Good question! Thanks for submitting this question in one of Constant Contact's recent nonprofit webinar!
With an email newsletter being far more inexpensive than a paper newsletter and allowing for more regular and personalized communication with your supporters, I just suggest starting by reaching out to those you have an email address for to see if they are interested in receiving your email newsletter. Send them a short email reminding them who your organization is, that you are about to start an email newsletter, explain the value they can get from it, and include a link for them to sign up. Constant Contact provides you with a free, customizeable sign up form you can link to.
Send your email newsletter to those supporters that signed up for it, and send the paper newsletter to those supporters that didn't sign up or that you don't have an email address for. Make sure to include the link to the email sign up form in your paper newsletter and encourage those supporters to sign up so more of your budget can go to the cause instead of paper communications.