Should I test length, personalization, emojis, or tone?

All these elements deserve testing, prioritized by likely impact and your specific audience:

Personalization typically shows strong results. Testing name inclusion, location references, or behavioral triggers often reveals significant lifts.

Tone tests (urgent vs casual, formal vs friendly) often show meaningful differences because they affect emotional response.

Length tests depend on your audience and content. Some audiences prefer concise, others respond to detailed subject lines. Test to find your baseline.

Emojis are polarizing. They can dramatically increase opens for some audiences and decrease them for others. Worth testing but do not assume they help.

Build a testing roadmap that systematically explores each element over time rather than testing randomly.

Start where you expect the biggest impact. For most senders, personalization and tone beat length and emojis, but your audience may differ.