Random testing wastes time. Here's the priority order for maximum impact.
Test Priority Order
1. Subject Line (Highest Impact) Affects open rate by 30-50%. Test first.
- Length (short vs medium)
- Personalization (name/company vs none)
- Style (question vs statement)
2. Call-to-Action Affects reply rate by 20-40%.
- Low vs high commitment
- Question vs statement
- Specific vs vague ask
3. Email Length Affects reply rate by 10-20%.
- Under 50 words vs 100-150 words
- With vs without bullet points
4. Personalization Level Affects reply rate by 10-30%.
- Generic vs segment-specific
- Basic vs trigger-based
5. Sending Time Affects open rate by 5-15%.
- Morning vs afternoon
- Day of week
How to A/B Test Properly
Sample size matters: Minimum 100 recipients per variant to get meaningful data.
Test one thing at a time: If you change subject AND CTA, you won't know which made the difference.
Statistical significance: Don't declare a winner too early. Use a calculator to verify results are real.
Quick Test Protocol
- Split your list 20/20/60
- Send variant A to 20%
- Send variant B to 20%
- Wait 48 hours
- Send winner to remaining 60%
What NOT to Test
Don't waste time testing:
- Font or formatting (minimal impact)
- Signature details
- Minor word changes
- Things that don't scale
Focus your testing energy on the big levers.