Here's how to do that:
1. "Dragon": Make a "D" handshape with your dominant hand, then bring your hand up to your forehead and move it back and forth as if you're breathing fire.
2. "Fly": Make a "V" handshape with your non-dominant hand and move it up and down in a fluttering motion.
You can sign "dragon" first, then follow with "fly" to indicate "dragonfly."
Remember, there are variations in sign language depending on the region and individual signers. This is just one common way to sign "dragonfly" in ASL.