1) Use a compelling Subject Line and avoid using symbols, exclamation points and words that trigger SPAM filters. Here is a link to the most common words in spam email.
2) Design your creative so that it can be read by both image- and text-based email programs. Include text behind all images so the email can be viewed whether images are turned off or on.
3) Limit your email length to one screen.
4) Test your message. One reason is to see how it will render in various accounts and on different devices - send a test to various email accounts - work, a gmail or yahoo account, view the message on your phone, etc. The other reason, and this is a big one... test your linkage - make sure everything clicks through and that your landing pages load.
5) Include an opt out. This is important! CAN-SPAM requires that messages contain some method of opting out of receiving email from the sender.
Implement these best practices and you are sure to see your deliverability and click throughs improve!