Email subject lines are the first – and too often the only -- piece of content a marketing email recipient reads.

If you’re delivering good content of actual use to that recipient, it’s a shame to have all that great work in the body of the email road-blocked by a thoughtless subject line. Give that line some love; optimize it to lift that click-through rate by engaging readers before they even open your missive.

1. Keep Your Subject Line Short

More than half of all emails are read on mobile devices, so optimize your email subject lines with those devices in mind. Studies from Campaign Monitor recommend subject lines of three to five words, approximately 65 characters.

2. Explain the Purpose clearly and honestly

A vague or misleading subject line causes a recipient to misunderstand the content. The recipient opens the email and finds unexpected, irrelevant stuff. Recipient marks email as spam. It may seem obvious, but your subject line should inform your audience of the actual content of your email campaign. Do not deceive readers or make false promises in your email subject lines. The one-time click is never worth the long-term loss. Build trust.

3. Use Engaging Language

The subject line is the hook. You can be honest and clear about content and still put enticing bait on that hook. Pose questions, play on words, write a one-line joke. Experiment with different calls to action.

4. Make It Personal

According to recent studies, personalization in email subject lines (such as including a first name or company name) improves open rates by more than 50 percent. Many marketers fail to take advantage of this, even though personalization is built into many popular email marketing software platforms. The success of this tactic will depend on the detail in your list. You will need consistent information about each of your contacts in order to fully utilize this feature.

5. Don’t Use All Caps or Excessive Punctuation

Email subject lines containing all caps or excessive punctuation are more likely to be marked as spam automatically by inbox filters and recipients.

6. Test everything, Including Emojis

Emojis are the latest trend in email marketing, but don’t use them casually. Successful emoji deployment requires testing and a little strategic thinking. If they are relevant to your email campaign and you don’t overuse them, emojis might trigger higher opens.

7. Use Title Case… Maybe

The jury’s out on the right way to capitalize within subject lines. Some studies report higher open rates overall from emails written in title case. (The first letter of each noun, verb and adjective is capitalized, as in the Title of a Book.) Others claim that sentence case (When the first word of the sentence is capitalized but the rest is not.) makes the email campaign seem more personal. Either way, capitalization practice makes a difference. Experiment with capitalization to see what works for your brand.

8. Include a Number (or Two)

Many studies have found that numbers in blog titles increase blog open rates and that the same goes for email subject lines. Studies from YesWare and Hubspot have reported increased open rates by including at least one number in the subject line.

9. Optimize Your Preview Text

Preview text appears below or beside your email subject line as a preview of your campaign. You have full control of this text and can use it as an extension of your subject line. Try posing a question in your subject line and answering it in the preview text. Or start a sentence in your email subject line and finish it in the preview text. Keep it short to make it more likely to display in full on all devices.

10. A/B Test to Find What’s Best for Your Audience

These email subject line tips provide great starting points, backed by data, for more successful email campaigns. But there’s no guarantee; some will be right for your organization or audience and some will be wrong. Most email marketing platforms offer A/B testing; use it. Try out email subject line variations on your audience and use the resulting data to drive your strategic and tactical email campaign decisions.