Like many others, I'm not a big fan of prompts, or of any kind of "practice" writing. Nor am I a big fan of planning short stories. Some few can make anything work, but prompts and practice make little sense to me. The best way to learn how to write good stories is by writing story after story of the kind you most want to write, and the best practice is the same.
As for planning, some make it work, but the test is simple. It's working if you're selling the stories, and it's not working if you aren't selling the stories. I don't know many successful short story writers who spend time planning, plotting, outlining, researching, or anything else along these lines.
As for pushing myself as a short story writer, I write stories that interest me, and try to write them as well as possible. I try to write great sentences, of course, but it's story and character that matter most, and most of my effort goes into making characters come alive, and telling a story worth reading.
I do think it's good to use different POV characters, to write outside your genre often, to write longer and shorter, to master, in fact, coming in at whatever length the story should be. Starting a short story and letting it turn into a novel is purely a matter of not knowing proper structure, and this pretty much always leads to disaster.