Dive summary: 

• The biggest challenge for an email marketer is to create emails that the recipients will actually open; these four tactics will help ensure your emails get opened. [see full list at Entrepreneur]
• One of the best things you can do is solve a problem with your email; set expectations when the user signs up for the emails that each one will hold information to help them solve problems. 
• Save them money is another big way to get consumers to open emails; using phrases like "free," "save," "sale" or "free shipping" can entice recipients. 

From the article: 

"It's possible to craft an email that both entertains and saves subscribers money, or one that can both make people smarter and save them time. But most emails focus on only one of the four themes."