Hi there!
I'm by no means an amazing short story writer, but over the years I wrote a couple of them. Most recently, a side-story for my main project. (If you'd be interested in reading it, let me know
It's around 1.8k words long.)
The biggest difference between a short story and a full-fledged novel is that there's a lot less detail and the storytelling only tells us the necessary stuff. In a novel, you can have multiple characters, plotlines, etc. But in a short story, it's hard to do that if you want to keep it, well, a short story.
I think that the biggest advantage of writing short stories is that you don't need to plan that much ahead. If you happen to find a plot hole, it's easy to go back 400 words and fix it. That's the biggest advantage of short stories.
Also, make sure that every sentence is meaningful and either propels the story or the characters. (This should also apply for novels, but there you can sometimes add sentences that don't move either and get away with it.)
And most importantly, just write. Don't stop halfway through and tell yourself: "This is not good." Finish the story, and if need be, rewrite it. You'll get there eventually.
It's not much, since I'm no expert but I hope it will be at least somewhat helpful.
Have fun writing!