Following could be some of the signals. However, its not a definite list.
1: Amount of ads per page
2: Location of ads, above the fold!
3: Interaction in terms of comments
4: Any unique good quality images?
6: Amount of G+ twitter fb likes on the story
7: Bounce rate of page?
8: Page speed
There could be more, but if you have really good back link profile, you might get away doing couple of things wrong on on-page