I like to follow simple rules when I'm rolling out a marketing campaign.  Rules provide a tidy framework to operate within and they help you focus on what's most important.  I've found that if you adhere to good rules you usually get good results.

Designing your emails with these two rules in mind will go a long way to making sure your marketing piece is as successful as possible.

1) The golden triangle - it's a hard and fast rule.  Westerners read left to right, top to bottom.  This creates a "golden triangle" on any piece in the top left corner.  This is where you need your message, hook and call to action prominently displayed.

2) Mobile optimization - this nascent rule is quickly becoming a requirement.  People are checking their email on their phones all the time now.  To adjust a marketer needs to keep emails less than 600 pixels wide to display well on a small screen.