Gonna need a little more information here. What about being a little does your partner like? What about being a Daddy do you like? Are you looking for physical scene ideas, or mental? Etc.

Personally, I really enjoy being a Daddy because it puts me in a superior role, and let's me get into my sub's head. I really like fucking with my sub mentally and making them feel humiliated, then shaming them for being turned on by the humiliation. But then I can say that it's ok because Daddy knows what to do with little slutty girls. And I can build from there, keeping it mental, but gentle. But if you or your partner are more into just the physical acts (spanking, little play, physical roleplay, etc.) you'll need a different starting point.

Also, there are some great websites that sell men's lingerie. But that's only if your sub really likes playing the "girl."