Keep it short
You want your readers to quickly understand what your email’s all about. Keep it under 30 characters – and if you can convey your point in only two or three words, even better.
Don’t be aggressive
The fastest way to get caught by a spam filter is to put an aggressive sales pitch in your subject line. Avoid using all caps or more than one exclamation point. Don’t make it sound like a sales play, but focus on the value to your subscriber. It should come across as a friendly offer, not a demand.
Make it personalised
As the saying goes, the sweetest sound to anyone's ears is the sound of their own name. Use a merge tag to include the reader's name in the subject line, singling them out and attracting their attention.
Ask a question
Questions help to build intrigue and can increase your open rate. If your reader thinks the answer to the question is in your email, they’re more likely to open it.
Creating a sense of urgency can get subscribers to open your email to make sure they aren’t going to miss out on something special. You could include mention of a limited time offer in your subject line or a count down to a particular date.
Stand out from the rest
It’s easy to forget how many emails your subscribers get from other companies. Your email might be interesting to you, but will it stand out? Think creatively about what makes your business or product special, and find a way to put this across in a way that’s unique to you.
Test across different devices
Remember that your subject line will probably get cut off at different points on different devices. Send a test to yourself and take a look before you hit ‘send’ – make sure it doesn’t get cut in a way that could change the email’s meaning or read as inappropriate.