According to a report from the McKinsey Global Institute, we spend about 28% of our workdays in our email inboxes. That's more time and attention than we give to any single website, social media platform, or possibly even to our spouses (oops).
Email also converts at a much higher rate than social media. When it comes to reads and click-throughs, email obliterates every social media platform.
Monetate's Ecommerce Quarterly (2012) found that email converts at 3.2%, whereas social media hovers around 0.6%. Mileage here varies though, because my own list converts at 55% for opens and 23% for click-throughs, whereas my tweets only convert at less than 1% for clicks.
The most important way to build your list is the most difficult--your newsletter has to be really valuable and/or interesting to your readers. So valuable that they want to share it with others. Save and use your best content for your list (not your blog, not your paid products).
Don't just tell people to sign up for your list on your website, give them specific reasons why it's valuable to them. Why do they need to be on the list? What's in it for them? What do they get specifically if they sign up? "Sign up to get my free newsletter" is boring and non-specific; don't use this phrase.
Make your website a massive funnel that drives signups as its main goal. Use your signup form as the star of your homepage. Place it after every page or blog post, and even make a landing page for it.
What's a newsletter landing page? A page where the sole focus is the signup box--listing what the newsletter is about, what its value is, and social proof, if there is some. Here's an example.
Use your mailing list landing page URL in your social media profiles, add it to your email signature, link to it from any/all guest posts you write, and even add it to business cards or print marketing. Anywhere you can mention your business, mention your newsletter.
The more important you make your list, the more important your subscribers will feel it is. Establish a schedule for emails and stick to it. Connecting with your list consistently should be a top priority for your business, not something you'll get to "later."
Customize the content in your signup process to make it sound like you. All newsletter software lets you tweak the wording on the confirmation email, the welcome email, and even the URL to which you send your new subscribers. Utilize this!
Also, write every newsletter like you're writing to that one person individually, not as a company selling to their "subscribers." Let your personality shine through, but don't be creepy about it (e.g., using a person's name six times in the copy).
People aren't interested in a boring free e-book to sign up, because that's what everyone does. What can you offer that's actually valuable? Different? Specifically made for the type of subscribers you want to attract? If you aren't sure what the incentive should be, think about the types of questions your audience routinely asks you. How can you package the answers in a quick and easy-to-digest bonus?
Remember, it's not the size of your list, it's the quality of the people on it. A list of 1,000 energized people, ready to buy your next product, is far more valuable than a list of 10,000 who rarely open emails and can't remember why they signed up in the first place.