For subscribers, your subject line is the most important factor in deciding whether or not they will take the time to open and read your message. Yet all too often, this crucial piece of copy is overlooked or pulled together at the last minute.

Paying attention to the subject line is one of the fastest ways to improve results from your campaigns. Here are some tips to help you take the best advantage of your subject-line opportunities:

Make it action-oriented

If you want a recipient to take some sort of action, be specific and tell them what they should do. Subject lines should speak directly to the recipient in an active tone. Start your subject line with words like: Learn, Download, Sign-Up, etc.

Make it concise

Although it may be tempting to include a full ‘sales’ message as your subject line, it’s important to know that some email clients cut off the end of subject lines that are more than 45 characters in length. Keeping the subject to 45 characters or less will ensure that it is fully visible to all your recipients.

Make it compelling

Think of your subject line as a newspaper headline that encourages recipients to click to ‘read all about it’. The subject line gives the recipient an idea of what is included in your message, but doesn’t give away everything you have to say. It must be compelling enough to grab the attention of the recipient as they quickly skim their inbox. Including the message’s offer and creating a sense of urgency are both well-proven tactics to consider here.

Align the subject with the message

The first couple sentences should be very consistent with the email’s subject line. They should add detail to and reinforce the compelling offer, and should also be action-oriented. We recommend including a link in the first or second sentence that sends recipients to the page you want them to take action on.

Avoid SPAM words

SPAM filters can be triggered for a variety of reasons, causing your email to skip recipients’ inboxes and land straight in their SPAM box. One of the easiest ways to avoid SPAM filters is by carefully choosing the words you use in your email’s subject line. Trigger words are known to cause problems and increase the chances of your email getting caught in a SPAM trap. By avoiding these words in your email subject lines, you can dramatically increase your chances of getting beyond SPAM filters.

Words like free, act now, offer or credit will almost always get flagged by SPAM filters. Our technology partner, Hubspot Inbound Marketing Platform, has published an exhaustive list of SPAM words to avoid. We suggest bookmarking and referencing the list when it’s time to write your next subject line.

Avoid punctuation

Some SPAM filters are also set to trigger when subject lines include ALL CAPS, or any punctuation, particularly exclamation and question marks, or odd characters like emoticons. Including these in your subject line will cause deliverability rates to decline and SPAM complaints to increase, so are best avoided.

Test, Test, Test

Develop three potential subject lines for your message. Mail 10% of your list using subject line A, and mail 10% of your list using subject line B. Once you’ve determined which subject line achieved the best results, mail to the remaining 80% of your list using the better-performing subject line. You can use an A/B test to test the following elements of the subject line:

Adding personalization to the subject line

The subject line length

The call to action

Words used in the subject line

Investing time before each campaign to develop truly effective subject lines is one of the easiest ways to improve your email deliverability, and ultimately, to improve the results you achieve with your email program.