1. Make your sign-up form easy to find
Make sure you have forms (as opposed to buttons) published in hard-to-miss locations on your pages, and on as many pages where the form is relevant. Remember that nearly every page on your site has the potential to be a landing page, particularly in the case of visitors arriving from search engines.
2. Provide a convincing incentive for subscribers to sign up
This is a great place to split-test copy and design. Testing will tell you what works best for you and your visitors.
3. Don't ask for too much information
It's tempting to ask for more information that might teach you slightly more about your subscribers, but the more information you ask for, the more hesitant many people will be to give up private information and to invest time into filling out your form.
Keep it simple. Ask for what you need to email your subscribers with your goals for personalization and segmentation in mind. Usually, "Name" and "Email" are all you need.
4. Use a thank-you page that does its job
The job of a good thank-you page, usually, is to transition subscribers from a Web site experience to an inbox experience.
Set expectations with subscribers about what they should expect to receive, including what your emails will look like in their inbox, and what they should do with it. This is especially important when using a confirmed opt-in process.
5. Understand why subscribers are leaving
Many email marketing software products provide an option for subscribers to leave feedback on their way out. Take to heart the concerns of these people and learn from them. Maybe you're not targeting correctly, or maybe you send messages too frequently.