In last week’s issue of Hints & Tips, we told you the story of Monogram Lane, an online retail business that specializes in personalized items like jewelry, car accessories, cell phone cases, and more.

Barbara Watkins and Cheryl Headley explained that one of the secrets to their success was effective use of email marketing, and subject lines that grab subscribers’ attention and compel them to open the message.

“We use catchy subject lines, but do not tell people in the subject line what is in the email. If they already know, then they won’t need to open it,” Barbara explained. “We once used the subject line ‘You’ve Come a Long Way, Baby!’ for our new technology Monogram Decals, and in the email we showed a picture of an antique typewriter and then a laptop and cell phone with the product we were selling.”

Barbara knows an important truth about email marketing: Many people decide whether or not to open an email based purely on the subject line. Yes, it’s true: You could have the most engaging content ever, a special offer for readers that will blow their minds, or the secret to world peace, but if your subject line isn’t a compelling one, then chances are good your subscribers will choose to ignore your message.

(Of course, it’s also true that a recognizable From line is equally important. If your subscribers don’t know who an email is from, they are more likely to hit Delete and never see what you’ve sent.)

So here are four tips for writing better subject lines that will capture your subscribers’ attention and get your emails opened:

1. Include numbers.
Headlines with numbers in them (especially odd numbers) work well because they imply easily digestible content. For example, “5 tips for balancing your budget” or “3 things you must do this weekend.” Putting a number in your subject line makes what you’re saying quantifiable and lets readers know exactly what they can expect.

2. Encourage action.
With any subject line, especially a promotional one, make sure to include a call to action. For example, mentioning a deadline (“Offer ends Friday”) or using text like “Respond now” will get people to open your message immediately.

3. Make your subject line social media–friendly.
If your email content is good, your chances of it being shared on social media sites go up. When it is, it’s the subject line that will double as your tweet, or the text in your Facebook post. Write a subject line that would encourage you or your readers to click on a link to learn more (i.e., something that says more than just “Our August Newsletter”).

4. Have fun.
Follow the lead of Monogram Lane and treat your subject line like a tease. Of course, if you do this, then it’s critical that your From line be recognizable one. Not sure if a more fun subject line will work? Test it: Divide your email list into two groups. Use the same content for both groups, and send a “normal” subject line to one group and a more fun one to the other group. Then compare open and click-through rates to see which subject line performed best.

What have been some of your most effective subject lines? I’d love to hear them. Post your thoughts in the comments below.