@Louis wrote this tutorial on Adafruit Learning System on this very subject: Overview | Creating GIFs for SmartMatrix | Adafruit Learning System
And I wrote this one on using GIMP to resize and crop larger animated gifs down to 32x32: Resize and Crop · pixelmatix/AnimatedGIFs Wiki · GitHub
Feel free to share any gifs you create here, it’d be greatly appreciated! Animated GIF Collection