The fate of your email hinges on the quality of the subject line. A great subject line can get your email opened and read – meaning more conversions for you. An uninteresting subject line will get it sent straight to the trash or spam — which does nothing for you.

The best subject lines make your reader feel curious about the contents of the email. Don’t try too hard to stand out in the inbox; instead, use a strategy of simplicity – this is what stands out in the stream of emails people receive every day.

Need some more help writing the perfect subject line for your emails? Here are the Dos and Don’ts for creating the best email subject line.

DO

1. Clearly Identify Value

What kind of value does this email contain? Tell your readers why they want to open it.

You must make this very clear through your subject line, as this will convince your readers to open the email. Your subject line should immediately make it obvious to your subscribers how they will benefit from your email.

For example, a subject line that says “Increase your revenue by 15%” is way more valuable than “How to increase revenue.”

2. Keep it short and sweet

The length of your subject line is a very important factor. Not only are shorter subject lines easier to read, they’re also less at risk of being cut off midway by the email provider – not a good look.

A regular inbox usually shows only about 60 characters of the subject but if you're on a mobile, it's even shorter with only 25-30 characters visible.

Best practice? Keep your subject lines limited to 45 — 50 characters in length.

Also make your subject lines as straightforward as they can get. When your reader receives an email, they should immediately know what to expect from it. To-the-point subject lines get more opens.

3. Include Numbers

Numbers in email subject lines work just as well as they do for blog posts, which is really, really well. So use them.

People love a numbered list or a number that tells them something is going to be easy (e.g. “4-step process” or “5-minute video”). Numbers can summarize what the email contains, demonstrating to the recipient that it’s a manageable and useful read.

4. Ask a question

A timely, relevant question will often get more opens. If your email content is answering an important question your audience has, consider using the question as your subject line. Even if it’s a question the recipient didn’t know they had, seeing it in writing (in your subject line) might trigger enough interest for them to open up and read.

5. Use preview text

The preview text is the line of text that appears in your inbox, often in grey, alongside your subject line.

It's worth spending some time composing preview text that complements your subject line, as it’s basically an extension of your subject line. A well-thought-out, strategically crafted “sneak peek” can have a huge effect on your open rates.

6. Make a call to action

Action-oriented subject lines almost always work well. Your subject line should be written in the active voice in order to get your reader's attention. By including action words in your subject line, you’re telling the reader what you want them to do when they read the email.

Examples:

• Watch Beyoncé in concert
• Download affiliate marketing whitepaper
• Shop the '90s trend

DON’T

1. Lie (or stretch the truth)

It might be obvious, but it’s a big one: never, ever, ever try to trick your subscribers.

Don't make false promises in your subject line that have nothing to do with the content of your email. This is not only spammy, but you will lose your subscribers' trust.

Don't attempt to get your readers to open an email that doesn't deliver on the promise. Keep it up and you'll almost assuredly end up in the dreaded spam folder.

2. Use the wrong words

There are some words that will get your email sent straight to the spam folder before your recipient even has a chance to read your subject line. Here are a few:

• Offer
• Free
• Credit
• Limited Time
• Act Now

Additionally, seemingly innocuous words such as Help, Reminder and Percent Off might also negatively affect your open rates. Check your words against a list of trigger words, like this one from HubSpot.

3. Use these other spammy strategies

In addition to certain words, there are some other techniques that will land your emails in the spam folder. If you want your emails to get opened, don’t do the following:

• g3t 2 Cr8ive with numbers and characters
• Overdo the exclamation marks!!!!!!!!!!!!!
• Use @#!**^$!@ expletives
• USE ALL CAPS

This is also a matter of simple email etiquette – it’s obviously sneaky, and no one likes that (including the recipients on your email list).

4. Be generic

Most of us have a lot of data about our audience and this should be used to personalize your email subject line. One way to do this is with location. For example, “New Store Opening in Cleveland” is great because it's relevant when you send the offer to your readers in and near Cleveland.

On the other hand, “New Store Opening” is much too generic and doesn’t really pique any interest.

5. Be Anonymous

Don’t forget about the From line. This is just as important as your subject line. Again, keep it simple and use it to identify who you are to the reader.

Make sure it’s a name – yours or your company’s – that the reader can recognize immediately. Keep this consistent and try not to change it often.

6. Use Filler Words

Don't bother with using words like “hello” or “thank you” in your subject line. These simply take up space in what is already a limited (remember? 45-50 characters!) slot.

Use your subject line to to convey your message as shortly and clearly as possible, as outlined above. Save the greetings and other filler words for the body of your email.

The Ultimate DO: Test it

The most vital DO of email subject lines is to test them. Send out a few different variations to see which one performs better. Constant testing will improve your open rates and make you a better email marketer.

For example, try sending the very same email with two different subject lines to two groups of subscribers and see which one gets better results.

So you’ve followed all the best practices and have the perfect subject line. Does this guarantee all of your emails will be opened? No way. But it does guarantee that more of your emails will get opened.

Email marketing is subjective. You can’t please all of the people all of the time. But by following these dos and don’ts, you can please most of them, most of the time. If 85% of your email list opens and reads, consider that email a success.

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This guest post is courtesy of Simon Slade, CEO and Co-founder of SaleHoo.