If limiting your soul-baring tweets to 140 characters is a challenge, think smaller when it comes to your emails. Much smaller: Smart phones only display five or six words of your email's subject line, so the gist of your message should be conveyed in about 20-30 characters when in portrait orientation.

Being concise is already a great parameter to have in place if you’re a known rambler (like moi), but you could be missing out on business if your subject line runs on or doesn’t grab attention. Smart phones don’t have preview panes, so it’s important to use what you’ve got: a clearly identified from name that builds trust and a short subject line that does its job of getting the email opened. Put the most important information first, and be aware of truncation: A subject line like Free gas at your Mapco station for one lucky winner could display as Free gas at your Mapco station.

From my own inbox:

You had me at "happy hour," with 35 characters total.

The entire subject line of 27 characters displays on my iPhone. This also lets me know that the email makes sense for smart phone use.

In full, this one reads Up to 74% off artisan-inspired furniture, high-style home designs, distressed decor, The Farmhouse Kitchen & more -- Hello, run-on: 113 characters. Luckily, the from name for this biweekly email is consistent, so I know it isn't spammy, but it still doesn’t grab my attention. Delete.

A version of this piece originally appeared in Emma, Inc.'s blog.

You might also be interested in:

• Why you should narrow your content's focus
• How to share compelling data without boring people to death
• Why your emails turn people off