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
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Mail Tester
Spam-check your emails before they send -
Postbin
Debug webhooks easily -
SenderScore
Check IP reputation -
MXToolbox
Troubleshoot DNS issues