Emphasizing Texture:
* Her hair was like springy coils of yarn.
* His curls were as tight and bouncy as a Slinky.
* Her hair was like a cloud of soft, fluffy sheep's wool.
Emphasizing Appearance:
* Her curls were like a cascade of golden ringlets.
* His hair was as dark and rich as a chocolate swirl.
* Her hair was like a halo of auburn ringlets.
Emphasizing Movement:
* Her curls bounced like a playful puppy's tail.
* His hair swayed like a field of wheat in the wind.
* Her curls danced around her face like twirling fireflies.
The best simile will depend on the specific type of curls and the image you want to evoke.