1. Use a consistent "From" field.
2. Have permisson to contact the recipient.
3. Never spam. Avoid spam trigger words.
4. Follow best practice email marketing techniques.
5. Monitor the blacklists.
6. Don't use carbon copy to lots of recipients.
7. Personalise the "To" field.
8. Don't keep mailing to someone if they have unsubscribed.
9. Don't use a mailing service that tolerates spam.
10. Remove bounces from your list.
11. Don�t use the recipient�s email address in the subject line.
12. Avoid using words that appear in Outlook�s Junk Filter list.
13. Don�t use multiple exclamation marks or dollar signs.
14. Ask recipients to add your email address to their "trusted sender" or "whitelist" list or Address Book.
15. Don�t use excessive capitalisation.
16. Avoid javascript, embedded forms, and hidden text in HTML emails.
17. Prefix all links with http://
18. Don�t use an IP address in links instead of a domain name.
19. Don�t mention spam laws compliance.
20. Block generic email addresses from your list ([email protected], [email protected], [email protected], [email protected], [email protected], [email protected], etc.)
21. Use confirmed opt-in (ie. send a confirmation email whenever someone is added to your list).

Source: Emailtools