Marshal Twilight's (Slightly Pretentious) Guide To Writing Clopfiction [Link]
https://docs.google.com/document/d/11gS31BQTdzDKDeMXI1-sxTOfCsv44_jDOynNgwhu1gc/
An excellent guide to erotic writing. Even though it focuses on one particular genre, much of it can be applied to all types of erotic literature.