Submit to horror magazines. Publications like Apex Science Fiction and Horror Digest and HP Lovecraft’s Magazine of Horror accept submissions for publication, and Apex is currently looking for submissions (although not simultaneous ones). Check out their websites for submission guidelines, be sure your work is pristine (no typos or errors) and submit. Read the magazines so you know what type of material they are looking for.
Submit to horror e-zines. The standards and accessibility of e-zines are usually a bit looser, and this is a great way to get some credentials and make some contacts. Look under Resources for a terrific list of horror e-zines you can check out.
Consider graphic novels. Graphic novels (or comic books) are becoming very popular and sophisticated, and publishers need new story lines. Go to your local comics store, check out the horror comics and take note of their publishers. Look for submission guidelines on their websites and get going!
Go to the bookstore and look for horror anthologies. Publishing houses like Essex Writers' & Artists' Guild need short stories for their anthologies, including the recent title "Nobody: An anthology of Dark Fiction." Once you find an anthology, look up its publisher online and read the submission guidelines.
Network. Join a horror writers' group or fan site and talk about your publishing dreams. Be careful not to divulge your storyline, but other fans may have some suggestions for you on how to share your story.
Submit to a small independent press. Although the pay and exposure may not be what the big publishing houses or magazines can offer, getting your first story published is a huge success, and will help you get future publishing gigs. Check out "The Writer’s Guide to Book Editors, Publishers, and Literary Agents" and look under the Horror genre.
Enter a contest. Many horror magazines host writing contests; winning one and getting your story published is a great accomplishment. It also looks good on future query letters, so get out there and get some exposure!