Why, blood, sweat and tears of course.
oh yea, great content and quality traffic doesn't hurt either ;)
Honestly, have a vision, find a niche that you really enjoy and bury yourself in learning every aspect of it. Then create blogs, market within the rules on MySpace, buy keywords (which isn't free but will be profitable if done correctly) and do everything you can think of to promote your product/site/vision.
My biggest rule of thumb to being successful in online adult is to diversify and not put all of your eggs into one basket.
