The top 50 does tend to shake up a bit. Any story that’s on a weekly shelf (including contest winners) has a good chance of getting into the top 50, but you do tend to notice that once the shelf is over, a lot of those stories will drop back down a bit. When I think about stories that NEVER leave the trending I think of Chain Reaction, The Teacher (Mette’s version), My Episode Lover etc. The interesting thing with those is that they’re all actually complete and have been for a while. You tend to notice that once a story is complete, it will gain a lot of reads at first then start to drop. But those stories have all stuck around the top (they’re not the only ones).
If a story isn’t complete, it has a better chance of staying at the top providing that the author provides continuous updates.
1. What originally made that story hit the top 50?
It could be a number of things. Being on a shelf is a massive advantage.
Having a decent amount of episodes and getting “lucky”. By that I mean: Let’s say a story has fifteen episodes. If a few people binge it at the same time it will quickly climb the ranks. The higher it goes, the more people that will see it and the more likely it will climb. Does anyone remember the story “The Nerd Makeover”? It was a mobile-created story that pretty much came out of nowhere from an unknown author and made it to the top 10 trending pretty quickly.
Other factors: The title and the topic. A lot of the trending stories do have similar themes.
2. Is there a common theme with the top 50 (of any genre) stories?
Gang stories dominate nearly every genre lol. In the overall trending section, nearly every story includes either a gang leader, bad boy or popular boy, nerd makeover, pregnancy or teacher. Most, if not all, of the top 50 are from the romance or drama sections.
2a. Any common choices? Style? Narration?
Usually just romance choices (who to be with). More and more Limelight stories seem to be creeping into the top recently but at the moment, I think INK is still the most common style.
3. Should these stories stay up in the top 50 forever and ever?
Well, you can’t really control what people like to read so yes. If people still continue to read these stories and keep them in the top, then they deserve to be there.
4. Are most of the top trending stories the same author?
You do tend to see the same authors up there frequently and often with more than one story.
5. Cover wise, is there a trend?
Covers of popular stories seem to have either nicely edited characters (rather than just the basic characters on a background) or even artistically drawn ones.
6. Episode length wise, is there a trend?
30-50 episodes that are roughly 10 minutes.
7. Does ‘Art’ or ‘Edits’ help? Is this fair?
I don’t really think they help to be honest. I personally don’t care if a story has artwork and whether it does or not wouldn’t impact my decision to read the story. Using special art scenes is “fair”. Sure, not everyone can afford to pay for an artist but that’s life 
If you can’t afford it, it’s not like you need it to make your own story great.