Include an even balance of images and text. The email campaign that is sent as one image tends
to end up in a Junk or SPAM file. With images turned off a one image email will look something like the invisible man. You know he is there, but just can't see him.
Avoid gimmicky phrases like "Act Now" and "Special Clearance" in your emails. Spam filters look for these key words when diagnosing a potentially unsafe email.
Avoid invisible text
This is another trick spammers use and has become an instant flag for spam filters.
Make it compelling
A no-brainer, but often overlooked. The more compelling your text is, the more your recipient will ignore possible design problems, be less likely to hit the delete button, and more likely to click your call-to-action. If your emails rely on the images to make a sale you might be dissapointed.
What do you like?
Sounds simple, but if there are emails you like then you will probably find other people do too. If you hate emails that you have to scroll for days to get to the bottom then there is a fair chance other people do too. No one has a patent on great email design so learn from the emails you receive that you like. We are not cureing cancer here even though some companies might make you think they are.