1. Being Too Vague: Avoid subheadings that don't provide clear information. 2. Overloading with Keywords: Focus on natural keyword integration. 3. Ignoring Consistency: Ensure that subheadings align with the overall email content. 4. Neglecting Mobile Users: Make sure your subheadings are readable on mobile devices. 5. Skipping A/B Testing: Always test to find what works best for your audience.