1. Use Media Queries: Media queries allow you to apply different styles depending on the device's screen size. This helps you adjust the layout and font sizes for different devices. 2. Flexible Widths: Use percentages instead of fixed widths to ensure elements resize smoothly on various screens. 3. Scalable Images: Use CSS to make images responsive. This ensures they resize correctly on different devices without losing quality. 4. Test Across Devices: Use tools like Litmus or Email on Acid to test your emails on multiple devices and email clients to ensure they render correctly.