Even though sharing email content with social networks and sites is still a new concept for most people, enlisting your subscribers to spread your message to their networks is rapidly becoming a standard email marketing practice.

My previous Engagement Marketing blog post explained why people share content with family, friends and peers and revealed the general qualities that make one email shareworthy and another one not.

This time I'll outline six design and content ideas that can help increase the shareworthiness of your emails:

1. Target the right social networks and media. The hottest social site on the Internet might not be the right fit for your subscribers or market niche.

2. Explain how to use your social-sharing feature in your welcome email and in regular program emails. Include instructions in both the welcome email and the first few email messages you send that include a sharing function. Then, either link to an explanation page on your Web site, or put instructions in your email footer and link to it using inline navigation.

3. Test the share function design, location and copy. Use text links and the social networks' logos to be sure people see them with or without images enabled. Also, test which locations of the share links within your emails deliver the most clicks and shares.

4. Highlight shareworthy content. Make your content actionable and easy to read. A European airline saw strong sharing results with a compelling and simple free-travel offer: "100% Discount for Your Beloved One."

5. Track how readers use your social-sharing features, and then use that information to refine your content. Over time, consider segmenting out your high-value or frequent sharers from the rest of the pack, and send them special offers or content.

6. Test, refine and test again. Like everything in email marketing, what works for one company might fall flat at yours; so, test everything.

I go into more detail about these tactics in my latest Email Insider column, "More On Making Your Emails Shareworthy."