If you want to be a writer, or to improve your writing and your chances of being published, you need to read.
Read all kinds of books, including those which you might not usually choose for yourself. You can learn as much from authors whose work leaves you cold as you can from those you instinctively love. You will discover ideas, methods of plot construction and literary styles which you many not have thought otherwise thought of. Some of these you might choose to adapt for your own work; others you might make a point of never using on pain of death. But you will have given yourself the opportunity to analyse which aspects of any particular book worked and which didn't, in your opinion, and to make your own creative choices based on this.
The publishing world is a fickle and is currently undergoing huge changes. The pros and cons of traditional publishing vs. indie publishing will be the subject of a different post. If you are aiming for traditional publishing then you need to know - not guess! - what kinds of books and short stories are currently being published by which publishers. The only way anyone can know this is by studying the market. There are lists publishers and the kind of work they look for, such as in The Artists and Writers Yearbook. Another option is to take a notepad down to your local library or bookstore and make a note of which publishers handle the kind of material which is similar to your own work. Through reading a variety of books, you may well already have a good idea of this.
If you're aiming short stories at specific magazines, then read a few copies of it before submitting your work. Otherwise, you may as well aim at a dart board while wearing a blindfold.
I've yet to meet a good writer who isn't also an avid reader. This isn't to say that there aren't any, however. Some writers avoid reading their favourite novelists while they are in the midst of writing first drafts so that their own style isn't influenced too directly by anyone else. Others have said this isn't a problem. All any writer can do is experiment and see what works for themselves.
Wednesday Writing Tips #2: Edit Your Writing.
Wednesday Writing Tips #1: Write!