Email marketing is an effective tool for businesses of all sizes. According to the Direct Marketing Association, when it comes to purchases made as a result of receiving a marketing message, email has the highest conversion rate (66 percent), which beats other forms of marketing like social media, direct mail and more.

But, many first-time marketers run into trouble when trying to build their email marketing list. As was described in an article last week, using a paid list can be counter-productive and ruin the reputation of the sender.

The key to getting consumers to sign up for an email list is offering something of value that makes it worth their while. This is easier said than done, when many consumers are already oversaturated with emails and don't want any more unnecessarily. However, a recent study from Adestra found what incentives work best for motivating consumers to sign up for email lists.

Adestra teamed up with eConsultancy to survey more than 1,100 marketers and used data from several years worth of email marketing campaigns to see what worked best for each aspect of the email marketing cycle, from gaining subscribers to getting people to engage.

Unsurprisingly, Adestra's study of U.S. consumers found that financial based incentives worked best for getting people to sign up. Of the people surveyed, most (85 percent) said they sign up to marketing emails in the hope they will receive some sort of discount or promotion.

The study also broke down which types of promotions performed the best with audiences. The top types of promotions consumers in this survey wanted to see were percentage-off offers (35 percent), free shipping (20 percent), free trials (14 percent), and dollar-off promotions (14 percent).

The analysis of the top promotion types reveals some helpful tips that marketers can use in their emails. For example, though everyone like "Free" things. Free trials under perform compared to other promotions because people associate these plans with annoying-to-stop subscription plans. Also, it's important to note that people were twice as likely to want to see percentage-off offers (e.g. Save 25 percent), rather than see dollar off coupons (e.g. Save $10).

There are other useful incentives, though they aren't as powerful motivators as financial incentives. When compared to those who want financial incentives, only half as many people (41 percent) in the survey said sign up to keep up with new products or services. That's still two out of five consumers, which is a sizeable demographic.

Additionally, more than a third (38 percent) will sign up purely because they love a brand and just over a quarter (27 percent) subscribe so they can take part in product research. The point of all this data is that there are a lot of ways to get people to sign up for emails and to open the messages when they receive them. If you give your audience what they want, they will come to you.

This focus on subscribers is important. Email subscibers are more than just a target audience. They can be just as useful to a brand as social media followers and fans. According to QuickSprout, email subscribers are 3 times more likely to share your content via social media than visitors from other sources.

So though email marketing can be difficult at first, it's worth the effort to build a subscriber base of people who want to get discounts and information about your products and services.

For more information about consumer attitudes, read this article on what consumers want from digital marketing when shopping in-store.