What i did? Well when i have a idea that i think somebody else could like too i throw it into a website, then throw it out there and see what people think. Sometimes i get valuable feedback and can improve, sometimes it is good as it is.
The only "secret" other than user generated content (what makes it actually passive) for me is to never stop trying. I have like 50 in use domains right now, many which i did not extend because they did not pay for themself after a year.
My site is only 1.5 years old. Revenue was stable that time. I think the biggest break was before that. But my site is also not "made for adsense" which was what google mostly penalized.
Its more like a forum, but not one. Users can post their own content and others can vote and comment that. Plus it has a huge searchable database.
The problem with static sites (i have those too) is that google loves site updates as often as possible. A site that is good ranked today can be killed by a more dynamic one next day.
The only "secret" other than user generated content (what makes it actually passive) for me is to never stop trying. I have like 50 in use domains right now, many which i did not extend because they did not pay for themself after a year.