Slow and steady. Subtle hints, in conversation and in bed.
Though, my best sexual encounters ever were with this one girl... we were friends for a while first, but flirting a fair bit, kind of circling each other. One night when we were hanging out, we basically just played a simple game of asking one question, answering another... inevitably, it turned to the sort of things we like in bed. Even then I wasn't completely forthright, but it was clear that I was dominant and kinky, and she was submissive and yielding
We knew right then that we'd be great together in bed.
Moral of the story is, I tend to approach it slowly and gradually in most cases, but there probably IS something to say for the "frank discussion" approach.