A lot of people treat email subject lines and headlines as an afterthought - something you toss in last minute just for the sake of having. But this is a huge mistake. Advertising Guru David Ogilvy said that 80% of your audience will read your headline and nothing else. If he were still alive today, he'd probably say the same thing about email subject lines. You can spend hours crafting the perfect body copy, but nobody will ever read it if your subject line isn't compelling enough to get them to open. So don't treat your subject line and headline like an afterthought. They're probably the two most important parts of your email.
Keep it short.
Most email inboxes reveal about 40-60 characters of an email's subject line. But mobile devices typically show only 25-30 characters. And according to Business Insider, about 50% of emails are being read on mobile phones. So shorter is definitely better. Try to keep your subject lines around 30-40 characters long.
Write it last.
Of course, you can write the subject line and headline first if you know what you're marketing so well that your copy flows naturally no matter where you begin. But for most people, moments like those are few and far in-between. We recommend you start by writing a draft of the body copy. This will help organize your thoughts and give you the raw material you need to find your creative hook - that key selling-point that you can base your headline and subject line on. After you've found it, take some time to craft your headline and subject line based on that hook. Finally, rewrite your body copy to fit with your final headline.
Appeal to emotion.
You may think that if you give someone a logical reason for buying your product, they’ll be more likely to buy. But consumer behavior research shows that people make buying decisions based on emotion, and then use facts and logic to justify their decision after they’ve made it. Here are a few ways to appeal to your readers’ emotions in your headlines and subject lines:
Self Interest (what’s in it for the buyer?)
Curiosity (a compelling question that makes them click to find out more)
Urgency/Scarcity (Limited quantity and limited time offer)
Remember: Your headline is a single sentence that should make your readers say, “I want that,” or at least, “What the heck is that?”
Need some inspiration? Here's a link to Digital Marketer's 101 best email subject lines of 2016