What are the best practices for email subject lines?
There is no practices. You just create a line incentive enough to get clicks.
Descriptive yet to the point in short sentence always work.
Keep Your Audience (and Your Goals) in Mind
Localize and Personalize
Test Keywords and Phrases
Keep It Short and Sweet
Use Groups and Segments
Convey a Sense of Urgency
Offer Value
Use Numbers
Engage With Questions