Loren McDonald offers 20 HTML design tips in three key areas: format, functionality and usability. He covers issues that affect how your message appears, including coding, images, message width and file size.

Format:

• Code emails by hand if you can.
• Avoid nested tables.
• Do not use canvas background images.
• Host images on your Web site instead of embedding them in emails.
• Avoid 1×1 pixel spacer gifs.
• Avoid using Cascading Style Sheets.
• Keep HTML Emails to 500 to 650 pixels wide.
• Keep message file size under 100 KB.

Usability:

• Validate HTML content.
• Avoid scripting if you can.
• Link to a Web version of your email message.
• Use image alt tags.
• Redesign the top of your email template so that readers will see your key content, even if they don’t see the images.
• Use horizontal layout rather than vertical.
• Incorporate both text and HTML and use alt tags, color and graphics instead of live images linked to your Web site.

Functionality:

• Provide lots of active links to content at your Web site.
• Navigation through your email should reflect your Web site navigation – don’t use different terms.
• Add functionality such as Send-to-a friend…carefully.
• Add a subscriber-management section to each template.
• Host rich-media functions such as inline audio, video or Flash on your Web site instead of embedding them in an email.

Read the full article here.