Subject lines are an oft-overlooked element of email marketing (and let’s face it, email in general!), but they are absolutely crucial. A beautiful marketing email with a poor subject line is like a job candidate with all the required skills who shows up for interviews in a rumpled suit—it makes a bad first impression, it shows a lack of attention to detail, and it disrespects the interviewer. Don’t be that guy; here’s how to craft the perfect email subject line.

Before we get into the content of a good subject line, let’s talk about the length. If you struggle to squeeze everything you want to say inside the 140 characters of a tweet, then you’re in trouble when it comes to subject lines. Research from Constant Contact says that subject lines with less than 50 characters have open rates of 12.5% higher than those with 50+ characters. If possible, try to go even shorter (25 to 40 characters, or five to eight words). This will prevent your readers from having an attack of tl;dr before they even get to your content.

Now let’s hit the content for those scant five to eight words you’ve got. A call to action is important because people won’t act unless told to do so. Think about what action you want recipients to take (even if it is something as small as just opening your email). That call to action doesn’t have to have an instant effect on your business (e.g. buy now!), but it should be a small step of pushing people through the purchasing funnel.

This call to action could take the form of something straightforward like “Our fall collection is now in stock,” or you could be a tease and say something like “We’ve got a new collection and we think you’re going to love it!”

Another way to jazz up your subject lines is by incorporating a pop culture or current events hook into your subject line. We’ve talked about newsjacking here before and subject lines are a good place to do it, like this example from Frontier Airlines earlier this year.

Just be careful that you don’t get too clever with your newsjacking—don’t stray too far afield from your message or promise something you’re not delivering. If you’re building your hook around current events, please never ever use the latest starlets’ shocking exploit—at least, not if you want to be taken seriously.

I can’t tell you how many marketing emails I saw after Miley’s infamous performance last year that tried to capitalize on her twerktastic moment in the limelight. They didn’t work (and I am embarrassed I’m even using the word “twerk” on my blog!).

Moving on, remember the old axiom, “don’t do anything you wouldn’t want printed in the newspaper”? Here’s the updated social media version: don’t do something you wouldn’t want tweeted. Flip this around, and do things you want tweeted. If you have a social media-savvy audience try writing your subject lines like tweets and your recipients may reward you by sharing your email with their Twitter friends. For example, a subject like “The secret to email marketing” is far more tweetable than “we’re sharing one of our secrets to content marketing.”

Speaking of secrets, if you’re primarily sharing information in your emails (as opposed to discounts/coupons, etc.), write your subject lines like headlines. Words like “secret” and “tips” and “how to” are important here. Whatever you’re selling, position yourself as a consultant dispensing wisdom and counsel. Try these subject lines on for size to see what I mean: “Expert tips on outthinking the competition,” or “5 tips for developing your channel strategy,” or “How to use Twitter for B2B lead generation.”

Personalization can also be a powerful tool in creating compelling subject lines. Words like “you” or “your” area great way to personalize your subject lines (e.g. “6 tips on creating an editorial calendar for your blog”). A not so great way is putting your recipients’ names in the subject line. This is a common spammer practice, and if your lists are imperfect in any way, you’ll set yourself up for a marketing automation fail when you address them by the wrong name, or a misspelled name.

Lastly, whatever you do, always A/B test your subject lines to see what works best for you. If you have 2,000 people on your list, try sending an email with one subject to 250 people and an email with another subject to another 250 people. Send the subject line that performs better to the other 1,500 folks.

We’ve shared some things you can do. As a bonus, here are a few things NOT to do:

1, Avoid spammy words like “free” so your emails don’t get snagged by spam filters.

2, DON’T USE ALL CAPS AND INCLUDE EXCLAMATION POINTS!!! It’s obnoxious and also there’s a good chance spam filters will eat your email for lunch.

3, A call to action is great, but don’t over sell in the subject line. That’s the email marketing equivalent of bringing up weddings on a first date.

So there you have it, the onDemand CMO guide to effective email subject lines! Happy emailing!