First-hand experience

[Goddess of Passion]

I find it hard to describe how something (an orgasm, love, joy, pain, desperation...) feels when I don't know it from experience. It's possible to write about situations you've never been in, but not without a lot of research.

[JCullen]

Usually if I'm writing about something that I've never experienced first hand, I go through it mentally first hand. If it's something I would need to have experience doing to know how to write it, then I either read other fics on the subject, talk to someone who's experienced it or research as everyone else has said. It really all depends on how you personally absorb information and how that fits with your writing style...