I don't agree with what you say. Your writing gets better just by you writing even more.

Firstly I am no qualified master story teller to even attempt to give directions but more than that the whole idea of this writing challenge is not about the technicality, sentence usage or any other aspects of being better writer/pointing and correcting mistakes.
The idea of the challenge is to just conjure up stories. Stories that are in your mind but need you to give them a life. That's all this is. Just to have fun writing and pour your soul out.