5. Push the Envelope (or Inbox). Don’t be afraid to try subject lines that are more aggressive, creative, tantalizing or specific than you’re currently using. Try some new styles, and test them. Monitor the results across all metrics—open rates, clickthrough rates, spam complaints, bounce rates and unsubscribes—to make sure that a bump in your open rate didn’t lead to an increase in unsubscribes, bounces and spam complaints.