There’s no failsafe rule for writing email subject lines that convert people on your list into paying clients. But there are a few guidelines you can follow to get your emails opened and read more often.
When Mailchimp conducted a study on email subject lines (they’re continually monitoring what works and what doesn’t), they concluded that short, descriptive subject lines do way better than “splashy or cheesy phrases” (their words). You can view their email subject line best practices HERE.
Email Marketing is very much about testing and measuring, so experiment with different subject lines and see what works. If one is a dismal failure, it will at least give you an idea of what’s NOT working. There’s no right or wrong.