Aqua dragons are those that are proficient at swimming and most at home in the water. They usually look like crocodiles or have fins.
Flying dragons are those that are proficient at flying. They usually look like a bird-hybrid of a wyvern and have wings.
Gliding dragons are land dragons that can glide in the air for a set period of time. They usually have bat-like appendages.
Land dragons are great at roaming the land. They come in a wide variety of shapes and sizes.