It actually came up early in our relationship. She asked me what kind of porn I liked, so I showed her all the amateur stuff I was into, which then lead to me showing her the Forum.
She was a bit taken aback, because she'd never done anything like it before, but the atmosphere here made her feel confident.
We talked about it a lot before we started, and we started slow, just testing stuff out, seeing whether we liked it (especially if she was happy). And it kept getting more and more risque :)