I could probably come up with dozens of scene setups that work for me, but it's fair to say that many of them build some sexual tension before the scene starts. In most cases there is a reason that the sex shouldn't happen. Maybe it's with stepsiblings, maybe it's a boss and employee. In a lot of cases there is some family relationship. A couple that come to mind are rare scenes where the girl models clothes for her stepfather, uncle of someone like that. There was a DVD a few years ago called (I think) "I'm Engaged to My Father" and there were two scenes in there that really did it for me. One was with Megan Rain and Ritchie Calhoun. Megan is Ritchie's step-daughter and they go sailing together for the 'first time without mom' as Megan puts it. There are some great shots of Megan sunbathing and then masturbating on the foredeck. Then she comes back to the cockpit and Ritchie proposes to her. The second scene in that DVD that I like is with Riley Reid and Steven St. Croix. They're sitting at the kitchen table and the scene is that Steven had been with Riley's mom, which makes sense since he's her stepfather, and he's now dating Riley. Riley is upset that her mother is no longer speaking to her. Steven proposes.
In both cases, sex follows the proposal.
One thing that both scene play well, which adds to this for me, is that the stepdaughters are so excited to be engaged and dream about big weddings with family and the stepfathers are a lot more realistic and hesitant about that.
Anyway... the bottom line for me is sexual tension adds heat!
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