Following up on what David wrote...
- Make it easy for people to subscribe. Use a subscription form and put it (or link to it) on every
page of your site.
- Don't require too much information from subscribers. Just an email address will usually be enough. If you need demographic info, then try and keep it to a minimum.
- State up front that you won't sell or rent email addresses.
- Put samples of your newsletter on your site so it is easy for potential subscribers to see what they will be getting.
- Provide content that will keep your audience interested and wanting to open your messages.
- My favorite:
Find other sites that publish a newsletter that targets a similar audience as yours. Then, swap space on the "thank you for subscribing"
landing page that people see after subscribing to each newsletter.
For example, on my site after someone subscribes, they are automatically taken to this page: http://www.searchengineguide.com/subthanks.html
On that page you'll find my recommendation to subscribe to Jill Whalen's newsletter with a signup form. Jill does the same on her post-subscription landing page.
You don't have to limit it to just one newsletter that you swap with. Just don't overwhelm the visitor with choices or the response rate will go down. Expect the same from the sites you partner with.
- Along the same lines, find complimentary newsletters and swap ads for your newsletter.