At the tender age of 20 I wrote my first erotic story thanks to this book.
The recommended reading at the back then lead me to Anais Nin, and to quote a rather cliche comment, the rest is history.
I'm not sure if this book is still in print (first published 1995), but anyone who fancies having a dabble at writing any form of Erotica, I'd highly recommend it.
I bought this book by Elizabeth Benedict whilst editing 'A Love That Makes Life Drunk'. You would not believe the complications of writing about sex in the 21st Century - consider equality, HIV/AIDS, use of language etc. This book helped put things into perspective, avoiding rather embarrassing mistakes when writing not only a sex scene, but also the plot.
So, having these two books in your collection will help guide you to writing an erotic novel with a sexual reference every 100 words! Yikes!