By this point you should have at least two or three stories, each over 10,000 words and ready to go. If not, go write them, this advice is for people who have followed the previous steps enough to gain the experience to execute a decent story.
As I mentioned in the previous step, your third idea is probably what you’re going to be using for this part, maybe your second if you wrote an entire book for your first idea. Whichever you use, get others to read it for you and edit the hell out of it. This is because you need to make these short stories, which are generally the only stories accepted by competitions. Considering the amount they go through, this shouldn’t be surprising.
Next search online or locally for writing competitions specific to your genre, writing courses or short story anthologies you can submit to. This will take a while because of due dates and deadlines of competitions throughout the year as most are done annually. All while you’re doing this, do some investigating on editors, agents and publishers that represent the genre you write in. As tempting as it is, don’t submit anything yet.
My eighth piece of advice is: sell yourself. One of the things that’s going to be requested in most submissions is a short biography. For new authors you’re going to need all of the free cred you can get to convince an agent or publisher to choose you.