It’s often said that the toughest part of creating a successful email campaign is writing the subject line. Marketers agonize over it. It’s only one little sentence, but perhaps the most important sentence in the entire email. With your contacts’ mailboxes overflowing, your only shot at getting them to open your email is with a carefully crafted subject line. Just like deciding which articles to read in the newspaper by scanning the headlines, you need to convince them that your email is worth opening in just a few words. While there is no sure-fire formula, here are some tips that have been proven to improve open rates.

1. Keep it Short. A good rule of thumb is to try to get your message across in 10 words or less. If the entire subject line can’t be read in the preview pane, it’s less likely to be opened.

2. Identify yourself. Make sure your company name is in the “from” line. This helps separate you from spam and gives you more space in the subject line since you don’t have to put it there.

3. Make them curious! Try to entice your contacts by making them want to open the email to learn more. One good way to accomplish this is to ask a leading question in the subject.

4. Avoid words that are picked up by spam filters. The junk box is your campaign’s graveyard.

5. List key content first. Get the most important information across in the first few words.

6. Create a benefit. Will they learn something, save money, or have a problem solved if they open the email? Web 2.0 marketing is all about “What’s in it for me?”

7. Create a sense of urgency. Setting a deadline for an offer or putting a call to action in the subject line is likely to get you a higher open rate.

Even if you do all of the above, the most important thing is to test, test, test. Do A-B tests by splitting your contact list into different segments and sending different subject lines to each segment. Then, compare the open rates to see what worked and what didn’t. Look at past campaigns and see which subject lines got the best open rates. What did they have in common? Use yourself as a test subject. Make it a daily practice to analyze the subject lines in your inbox. Which ones did you open and which ones did you ignore? After a while, you’ll begin to recognize patterns and what seemed like an agonizing task will become second nature.

Jason Klass is the Internet Marketing Strategist at Vambry. http://www.vambry.com