SUBJECT LINE
Including the company name or brand results in open rates 32% to 60% higher than email messages without that branding.*
Focus on clear benefit, value proposition and credible solution. Be compelling, relevant, do not mislead. Be brief - no longer than six or seven words. Avoid spam-like language. Use company first in Subject line for email clients without prominent From fields.+

LOCATION OF LOGO
Above the fold, on the left.

TEXT TO IMAGE RATIO
The presence of artwork in email messages doesn't have a substantial affect on response rates.**
B2C all text - 4.7% click rate*
B2C image-oriented - 7.0%*
All-txt B2B messages had 54% higher click rates than those with equal amounts of text and images.*

LAYOUT
B2B postcard-style layouts received the highest click rates perhaps due to novelty.*
Newsletter B2C layouts generated more clicks than the postcard layout.*
But...
Only 12% of subscribers overall said a postcard-like image influences them to click. 25% of 18-24 year-olds said postcards DID inspire them to click while only 9% of those 55 and older said they responded to image-centric messages.**
Test layouts in multiple email clients.***

LINKS
Include between 6 and 10 links. More deteriorates results.*
Financial marketers often don't include links at all to protect recipients from phishing.*
Use absolute URLs.***

TYPE OF LINKS (text vs. image)
B2B emails with text links received 83% more clicks than did those with image links.*
B2C emails with images or images and text both receive higher click rates than those that don't.*
Visually highlight links with different color type to help reader navigate to CTA. Place a button link next to a text link is also beneficial.*

NAVIGATION BAR
If a navigation bar is included, for B2B emails it should be placed along the top, and for B2C emails it should be placed on the left-hand side.*

LIFESTYLE PHOTOGRAPHY
Don't use lifestyle photography for B2B emails.*

FEATURE OFFERS
Offer a specific dollar amount off instead of a percentage. Also, free gift offers have very high click rates.*

THE FOLD
The fold (content area viewable without scrolling) varies, but should be considered the top 400 pixels of content.

CALL-TO-ACTION
Place the call-to-action above the fold for B2B emails. This is optional for B2C emails as there is little decline in messages that require the customer to scroll down.*
Call-to-actions should be clear.***

EDITORIAL
Address recipients by name.***
Avoid "$" signs.***
Emphasize with words not exclamation points.***
Keep most important information above the fold.+
Proofread, proofread, proofread.+

DESIGN
Don't forget how the email might look in the Preview pane.***
Maintain brand consistency with other corp communications.***
Experiment with link placement to establish best location.***
Send emails as multipart/alternative messages so recipients and mail clients can determine if they want HTML or text.***
HTML and plain text parts should have corresponding content to get by spam filters.***
Test across all email clients, platforms and browsers.+

FORMATTING AND CSS
Do not style the body or head tags, the may be stripped or broken by the email client.+
Almost call email clients offer limited CSS support so embedded styling is the safest format to use.+
Multiple columns should rely on old table based coding methods.+
Links should have inline styling.+

FORMS IN EMAIL
Simply forms that don't reply on JavaScript can function properly in some email clients but with issues that should be researched and tested.+

IMAGE BLOCKING
Examine how email will look when images don't load to see if the audience can recognize who it is form, identify the brand without a logo, understand what message is about, identify value proposition, etc.****
Add "if you can't read this" link to top of email****
Make sure content is not one big image and insure the call to action is in text (as well as any images.)+

USABILITY Avoid horizontal scrolling. 600 pixels fixed maximum width reduces scrolling and optimizes printability.+ Do not use JavaScript or Flash in an email - outside lowest common denominator for success in most inboxes.+

EMAIL LANDING PAGES
Landing page should match the email in design.***
Prefill forms on landing pages if possible.***

SENDING
Avoid email marketing during the holidays.***

*Source: "Email Creative That Works" from SilverPOP
**Source: "E-mail Marketing Content Best Practices," JupiterResearch, November 2005
***Source: About.com Email Marketing Tips, Tricks and Secrets
****Source: EmailLabs: "When e-Mail Images Don't Load," Derek Harding, June 16, 2005
+Source: "Creative Guidelines for Effective HTML Email Templates" from Blue Hornet