I think the first thing here is content:
- you shouldn't have many many pics. They just ought to be different. For example if it is straight sex - show the variety of places, where sex takes place. Got the point?
- movies are important too. It's my firm belief that such a site should have many interesting movies - young girls screaming in action and so on. But here there is one trick to get surfer interested - there should be 6-8 free good quality short films, which should be changed once per 3 days or so.
The second thing is design:
- it shouldn't be too loaded and bright - just exquisite, pleasant and seducing. Understand what I mean?
- you should have everything arranged neatly without annoying things.
Anyway - do your best. And if you've already started - put your soul in everything you do.