How is an erotic writing prompt different from any other writing prompt? It has sex in it.
Erotica includes sex but isn’t just sex.
This means there is a story. Too many writers get into the sex and leave the story as the background.
Erotica should be sensual.
How do you especially like to be touched? What kind of touch gives you pleasurable shivers?
Don’t even start thinking about sex itself. Start with the touches which aren’t very intimate but get noticed and get you interested in having more.
For me it’s my back. A stroke down my back will always get my attention.