Building a list of responsive subscribers via a Web site that has a bit of traffic and quality content is surprisingly easy.

But sometimes, when working with users, we're surprised to see low conversion rates. So, we take a look into just why that might be.

Here are five factors to consider when growing your list.

1. Make your sign-up form easy to find

Too often, we find newsletter sign-up buttons on Web pages tucked away somewhere out of the obvious. When I see a page like this, my first thought is always "this must be a lower priority on the list of actions that the site owner wants visitors to gravitate toward."

That's a shame, because email, like no other technology, gives us the opportunity to turn one-time, anonymous visitors into engaged subscribers with whom we have the ability to develop beneficial relationships.

And yet, when I do speak with those with hard-to-find sign-up placements, I often find that they do understand the importance of email. They just don't have optimal placement for their sign-up forms.

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

For some sites, a form headline as simple as "Sign up to Receive Our Newsletter" does the trick for generating subscribers.

However, if there is room for concern about what will happen with the information that visitors provide, and whether their trust will be abused with too many emails, some people will not sign up.

I always wonder whether Web site owners have tested approaches that give more specifics, including privacy assurance and specifics about what will be sent and when.

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

When your main objective is to get someone subscribed to receive your newsletter, they shouldn't have to fill out a form that looks like something they'd find at their doctor's office.

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.

Wouldn't you rather know just a little less about a lot more subscribers?

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

So now you've got their name and email address. We're all done then, aren't we?

Sure, we can stop here if we're concerned only about "capturing subscribers" and list growth. But if we consider the other goals of our campaign, such as engaging these people who've expressed interest and keeping them interest, we need to consider the sign-up process as just the beginning of larger process.

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.

We see a lot of thank-you pages that are dead ends or which simply link back to the homepage. Successful marketers treat this page as the opening of a funnel that uses email and Web content together to lead to a sale or other objective.

5. Understand why subscribers are leaving

It's hard to fill a bucket with water when there's a large hole in the bottom. In the same way, it's hard to grow a list when large numbers of people constantly unsubscribe.

If you're noticing a significant or growing number of unsubscribes, you should spend some time thinking about why that might be. (See "The Top 5 Reasons Subscribers Opt Out of Email (and What to Do About It).") 

Many email marketing software products provide an option for subscribers to leave feedback on their way out, with a feature that forwards messages to you when they do. Don't filter these messages straight to the trash. 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.

For as far as you can take this information to improve your campaign for the long-term, some unsubscribes can actually be good for you and your campaign.

There's always room for improvement

Do these tips ring true for you as you take a look at your own sign-up form approach? Do you see obstacles that are keeping you from turning visitors into subscribers?

Remember that there's always room for more testing once you've laid the foundations for your campaigns.