One of the best resources is the blog Word to the Wise. In addition, below are some best practices from the major ESPs:
Where can I learn more about Deliverability and Email?
Where can I learn more about Deliverability and Email?
Other Helpful Resources
-
Mail Tester
Spam-check your emails before they send -
Postbin
Debug webhooks easily -
Google Postmaster Tools
Check Google Sending Reputation -
MXToolbox
Troubleshoot DNS issues