Keep it short. Subject lines are more important than ever. Keep them succinct and focused so they grab recipients' attention. Front-load the most significant elements, whether it's the benefit the message offers or the call to action.
Go light on images and HTML. Also, create a text-only translation of the email—and make sure the links in the text version work.
Make sure landing pages are optimized for mobile. Recipients who click through on an email should be able to access the additional information they seek through their mobile device as well.
Don't ask for too much information. Remember that recipients can't type as easily as they can on a desktop computer. Don't ask them to fill out multiple fields.
Consider responsive design templates. More marketers are including snippets of code that detect the user's device and adjust the email accordingly—for example, cutting it down to one column and resizing buttons.
Remember to include white space. Include extra space around buttons and links to account for “fat fingers.”