We all know how important subject lines are. Almost half of email recipients open email based on the subject line alone. More than two-thirds of recipients report email as spam based solely on the subject line. And—this one made me chuckle a bit—emails with no subject line at all have an open rate of 8% more than those with a subject line.

That last stat probably does offer one real lesson: that we are a curious people and subject lines that convey some mystery do well—no greater mystery than an empty space that is usually filled.

I've poked through some articles and surveys to find more suggestions on subject lines and emails. I just looked over to the BIMS schedule for any corresponding sessions and saw that Luis Hernandez, director of strategy for FDAnews, is presenting a session titled, Creating an Effective Email Series that Engages, Nurtures and Converts. I highly recommend this for anyone attending.

Some rules to craft subject lines by:

1. Personalized subject lines are 22.2% more likely to be opened. You can also use casual language or copy that implies some familiarity. But, be careful not to over-personalize. A bank teller chastised me the other day for not using my bank card for a deposit. So I slid my card through. "Oh I see it's your birthday this month, thank you for being with us 32 years, I see that you live in..." I was happier before using my card.

2. Focus on the fear of missing out. OptinMonster writes that "subject lines that include words that imply time sensitivity—like "urgent," "breaking," "important" or "alert"—are proven to increase email open rates. This seems like the digital equivalent of passing a restaurant or theater where people are standing in line. I don't want to miss out! OptinMonster also likes humorous subject lines, but that can be very hard and risky to do. Test first on others.

3. "Fascinate" with lists and how-tos. Writing for Mequoda earlier this year, Amanda MacArthur—now of Lantern—listed 4 subject lines "that are proven to get opens":

• The how-to – "It is nearly impossible to write a bad how-to email subject line";
• The fascination – "compelling, benefit-driven bullet points that motivate the reader to discover the answer... often include the words "discover," "secrets" and "amazing";
• The list – "Readers love lists because lists comprise convenient summaries: and
• The reasons why.

4. Try emojis in your subject line. Mequoda's Kim Mateus just posted an excellent article on this: "Earlier this year, one of our clients was the first to do some formal emoji subject line tests. In all but one test, the emoji subject line was either the winner, or had a modest (but statistically insignificant) lift. The lift ranged from 1.3% to 10.6%. According to a report by Experian, 56% of brands who have tried using emojis in subject lines increased their open rates."

5. Emails with "free" in the subject line are opened 10% more - though you do have to be careful about falling into spam. Those with "fw." were opened 17% more, but that's another thing to be careful about. Being deceptive can work once but is not a good long-term plan. We don't like to be fooled.

6. Focus on what's in it for the customer, not you. So, "Reminder to take our survey, it's important to us!" is not good. The benefit is not for the customer. "What is a benefit?" asked Jim Sinkinson of FiredUp Marketing. "A benefit has to have one of two elements—an emotional reward that makes you feel great or a tangible reward. What it is not is information, learning something or news."  (Sinkinson will be a co-presenter of a Pre-con workshop at BIMS on the subject of renewals.)

7. Use words that speak to your prospect's known problems or hot interests (also from Sinkinson) - (e.g., penalties, new cure, lawsuits, save money). What is going to motivate that person to become a member or subscriber?

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Ronn Levine began his career as a reporter for The Washington Post and has won numerous writing and publications awards since. Most recently, he spent 12 years at the Newspaper Association of America covering a variety of topics before joining SIPA in 2009 and SIIA in 2013 as editorial director…