If you're talking about a contract with Tapas, it's rare to get those outside of contests these days. You need thousands of subs and likely millions of reads.
If you're talking about getting a promotion on the front page of the community tab, that happens when the stars align and your story catches the eyes of staff. I had a front page promotion on one of my story when it was around 130 subs or so. But that's story was also in a contest and got a contract from it, so I'm not sure how it would have been seen otherwise.
Just so you are aware, even getting a promotion from Tapas is temporary. I gained a handful of subs from it and then that attention, too, died down. You will likely always be marketing your work. It's part of the game.