If you ever use email as a business tool, to market your products, or to apply for a job, then this post is for you.

Email subject lines are among the toughest of writing tasks. Like a newspaper headline, they should tell the reader about the content of the email — and then entice him/her to learn more.

There are no hard “rules” about writing subject lines, but these tips may improve your open rates:

Keep subject lines short.
The best email subject lines are short, direct, and compelling. Aim for fewer than 60 characters, including spaces and punctuation.

Be direct.
Get to the point. Avoid puns and catchy phrases, unless they relate directly to a specific campaign or promotion.

Be specific.
Include important details, such as web seminar dates or “reply-by” deadlines.

Include a call to action.
Do you want the reader to take a specific action? Then say so.

Choose short, active verbs.
“Use” is better than “utilize;” “grow” and “boost” are better than “maximize.”

Focus on the benefits.
Everyone wants to know what’s in it for them. Tell your readers what they’ll gain from opening your email.

Give a sense of urgency.
Are you making a limited-time offer? Is a deadline looming? Make sure the reader knows this.

Use English.
Abbreviations are GR8 for txt msgs. But if U R sending yr msg to an adult, pls use complt wrds.

Punctuate sparingly.
Write your subject lines as brief statements. Too many commas can trip readers up.

Punctuate sparingly, part II.
Avoid exclamation marks. (They’re the copywriting equivalent of shouting.)

With all of this in mind, here’s one way to approach to writing subject lines:
• Read the email from start to finish.
• Underline the single most important point (i.e., what is the email about?).
• Read the email again and underline the most pertinent facts (dates, deadlines, etc.).
• Review the facts you’ve underlined. Which ones are “must-knows”?
• Use the “must-knows” as the building blocks for your subject line.
• If appropriate, tell the reader what action is required.

Want to dig deeper? Check out Jakob Nielsen’s suggestions.