According to Scott Palubinsky there are three main aspects of email marketing: list quality, creative rendering, and reporting:

1. The  quality of your list is much more important than the quantity. Growing your list is important, but what is more important is growing your list by adding opt-in subscribers/customers who will positively respond to your campaign. By segmenting and targeting the contacts on your lists, you’ll have a much greater chance of reaching your desired audience and getting a positive and profitable outcome.  Once you have your list developed, be sure to keep it clean by managing bounces and non-responders.
   
   
2. Creative rendering can make or break an  email campaign.  Follow these guidelines for designing for the preview pane and keeping the call to action above the fold.  Test what your emails will look like in multiple ISPs and mail readers.  A tool like our Sender Score  Monitor Program can help with this.  Look and establish where problems with your HTML are occurring and ensure that the creative design of your emails is engaging your subscribers and not getting lost in the shuffle.  Your creative work may look brilliant in one ISP, but could lose its design integrity in other ISPs, thus preventing your message from making an impact on those contacts/subscribers.
   
   
3. Analyzing and adapting to the information gathered from your email reports is the best and most efficient way to improve the success of your email campaigns. The best reporting shows you open, click-through, forward and opt-out rates, as well as bounce reports and deliverability reports by domain.  More advanced reporting can also provide you with conversion data.  Use this reporting data to measure the effectiveness of your campaigns and show you what can be improved upon next time. 

Paying attention to these three truths can help to dramatically improve your email marketing program. 

Check yourself now: 

• Do you have a high quality list of subscribers that have specifically opted-in to receive your emails and who respond to the messages you relay in your emails? 
• Do you have a compelling email creative that is designed for the preview pane and that renders well across various ISPs?
• Do you have access to a comprehensive reporting tool that you check on a regular basis and use to improve upon your email strategy?

Source: Blue Sky Factory