Email marketing continues to deliver strong ROI, more than twice that of search marketing and the highest among all direct response methods, according to the Direct Marketing Association. Furthermore, it works to foster deep customer relationships, which can play to a company's favor well beyond the present.

Consistently expanding your opt-in list is one means of further increasing those returns, and the following five-step program is aimed at helping you achieve that goal.

Step 1: Remove the throes of risk and inconvenience

Before all else, you want to ensure that your opt-in process is completely user-friendly and that nothing stands to stymie your opt-in rates or turn users away. Use the following tips to help optimize that process:

Make it simple

Ensure your invitation to sign up is highly visible, your links are functional, and your registration form is both straightforward and easy to fill out. "Some of it comes down to how the landing page is organized and how the form looks," explains Chris Chariton, VP of marketing services and product management at GlobalSpec, an e-publisher that garners approximately 80,000 new registrants every month. "You may be able to get some lift by improving that process, by making sure it's easy and doesn't take a long time."

She suggests testing to find the right formula. On your website, for example, begin by positioning your call to action at the top left of the page, where the eye commonly begins surveying the page, then try other placements on the page to figure out where your messaging gets the most notice.

Also experiment with copy—not only wording but also size and type (font). And don't forget to test the particulars of your registration form—layout, design, copy, number of fields, etc.—to determine whether anything there is having an adverse impact on your conversion rate.

Don't probe too deep

Calm subscriber concerns by asking for only the minimal amount of information you need to make the program more beneficial for recipients—for personalization or segmentation, for example—and always assure users that you value their privacy, with a promise to never sell or share their information.

"You don't want to scare them off by asking questions that are too personal or complicated, or by simply asking too many. On the other hand, it's your primary chance to learn about your subscribers and tailor your campaigns to important segments of your audience," explains Jim Hitch, agency relations manager at email-marketing services firm Emma. He advises you "ask for what you need, then use what you ask for."

Blue Sky Factory, an email service provider, suggests starting with a simple request for the user's email address, then using a welcome email to collect additional data.

Give them a taste

Clearly explain what frequency and type of content recipients can expect, and allow them to preview a sample communication before they enroll.

Offer options

Enable your opt-ins to have some control over the communications they receive. Allow them to select preferences such as language, format (text or HTML), frequency (daily, weekly, monthly, etc.), platform (receiving communications via email, Facebook, etc.), and content topics.

Step 2: Insert value

Users want to know what they stand to gain by registering for your email communications—whether it's the value of your content, or some other incentive you plan to give them in exchange for opting in—and that benefit should be clearly conveyed both in your promotions and throughout the registration process.

The offer of value-added content will likely garner a higher quality opt-in, because the user is genuinely interested in your communications and not simply signing up for a free prize. That said, a giveaway might be the carrot you need to entice users to give your content a try.

Chariton of GlobalSpec suggests using an incentive that makes sense for your business. Free content such as whitepapers and case studies, for example, are low-cost giveaways that can be easily emailed to registrants; at the same time, they can be used to qualify leads, since interest in that content demonstrates a potential need for your services, she explains.

Step 3: Affix invitations to active engagement sessions

A recent study performed by ExactTarget in cooperation with Ball State University and the Email Marketers Club found that the most effective list-growth tactics involve organically "gathering" users' addresses during customer-initiated interactions.

"The best time to ask someone to join your list is when they're most excited about you and what you do," Hitch of Emma confirmed. He advises looking for "creative, natural ways to extend an invitation to join your email list right then, at the moment someone's most likely to say 'yes.'"

Here are a few places to start:

• The company website: Onsite registration was found to be the most effective tactic by the ExactTarget study, so it pays to make every effort to convert your visitors while they're there, on your site. Instead of a call-to-action on a single page, include it on every page of your site, in multiple locations on each page, and make sure it stands out, according to the email-marketing specialists at Blue Sky Factory.
• Social media: In addition to adding a link on the company blog, personally invite users with a link to your registration page as soon as they subscribe to your blog or connect with your company via networking sites such as Facebook, Twitter, and LinkedIn.
• Inbound call centers: Making requests during customer-initiated phone contact is another effective tactic, particularly for B2C businesses. Also encourage your customer-service staff to include an invitation and link at the bottom of all typed responses.
• Tradeshows: A high-performing B2B tactic entails asking attendees at tradeshows and conferences and keeping opt-in forms readily available on the show floor. "Collecting business cards at your booth is not an opt-in. You must ask their permission, as well," advises the Blue Sky Factory team. "Verbally set their expectations around frequency and content, and send that welcome email immediately upon their return."
• Point of sale: In-store promotions won't produce the greatest yield; once in place, however, they tend to provide ongoing service with minimal upkeep. To improve their performance, ensure your signs remain unobstructed and won't be pushed aside (if using table tents, etc.) and direct staff to actively ask patrons to sign up, suggests Josh Nason of email marketing firm SendLabs. Another solution (effective for other offline list-building campaigns, as well) is to incorporate text-messaging into the opt-in process so that shoppers can easily enroll right then and there.

Step 4: Scan for public data

When these organic tactics aren't enough, or when you'd also like to target customers who aren't currently initiating contact with you, there are append services such as FreshAddress that will cross-reference your list of customer postal addresses with its email-address databases. Matches are then invited to either opt in or permanently unsubscribe from your company's email communications.

Over the last few years, Cutlery manufacturer CUTCO has been able to add 726,000 email addresses to its list through a series of appends. Of those, around 20% have remained active subscribers over time, and while those accounts may not convert as well as opt-ins brought in through more organic means, they do perform better than the company's dormant list and continue to achieve a positive ROI.

For best results when integrating such new addresses into your email database, FreshAddress suggests the following:

• Only appending addresses of people with whom you already have a relationship
• Testing the waters by initiating email contact with 10% of your appended results, analyzing click-through and unsubscribe rates, and adjusting your approach as necessary
• Taking the time to reintroduce your company and the merits of your email program with a welcome email
• Expecting a few complaints and preparing your customer service team ahead of time
• Allowing for, and quickly honoring, unsubscribe requests

Step 5: Stimulate social activity

Leverage your existing base by including share options in all your email communications. These can entail "send to a friend" links, as well as prompts to post the content to social sites such as Facebook, Twitter, Digg, Technorati, and Delicious.

Although the ExactTarget study found these to yield relatively few new subscribers overall, they are very inexpensive tactics to implement, and you may be able to improve your own results by getting creative in how you present the option and motivate users to share.

For best results, be sure to add prominent subscribe links to all messages and postings, including the original communication in case recipients choose to forward the messages on their own. You might also consider offering contests, special offers and other perks to help spur involvement.

It's important that you take the time to develop a good email strategy before you start emailing customers. Otherwise, a misstep could cost you opportunities to communicate with your customers or damage your credibility. Check out Nine Email Tactics That Can Put You Out of Business for great examples of what NOT to do. As a Premium Member, you have free access to hundreds of Premium articles, case studies, templates, tools, research, and "how-to" guides to help you rapidly build effective marketing programs.