One of the most important metrics in an email campaign is the number of recipients who have opened the email i.e. Email Marketing Open Rates

The open rate is the ratio of the number of recipients who opened or read the mail to the number of recipients the email campaign was sent to.


There are other important techniques as well:

SUBJECT LINES:  One of the chief factors that contribute to open rates is subject lines. Short, expressive, and something that gives the reader a reason to explore the message makes a good subject line..subject line should be straightforward, avoid promotional phrases, CAPS, or exclamation marks in your subject lines.

Research, and avoid, typical spam words: 
Words such as “free” or “act now” or dollar signs can be a red flag not merely for spam filters; they also stand out as suspicious words to the recipient.

Choose the right “From” name and email address:  These should reflect a professional brand image to encourage recipients to open the email. The email should also be relevant to what you are offering to your customer, while also matching the appropriate company department.

Construct a well-structured message, that includes quality content with both text and images:
Do not use one large image as your entire message — make sure you have a good amount of both text and images in your message

Conclusion:
Though there are endless suggestions for improving open rates, these are some great starting points.
Following these suggestions might be all you need to kick-start your Email Marketing efforts and make your email campaigns more effective.