Best source of markets, articles on how to write for various kinds of writing; articles, books, varieties of fiction, scripts, etc. Also has sources for artists and poets. You can find the current Writer's Market in your local library. It's published every year, so you might find past years in nonfiction, and the current one in Reference, which will not check out, but you are free to look up what you need while there. Under copyright law, you may photocopy no more than the equivalent of one normal-sized chapter, so choose carefully. Especially, pay attention to the section on How To Format Your Manuscript. New writers often make the mistake of formatting their manuscript in an attention-getting way, by using fancy fonts, or packaging it creatively. You will find out in the articles, it is better to follow their suggestions and just mail it off in a box or manila envelope that looks ordinary. Your book will sell on the merit of your words, attention to grammar and spelling, and your writer's voice.
Don't get discouraged; 99% of manuscripts are rejected, mostly because the writer didn't use correct English, or spell well, or used weird fonts. Persistence will get you published, and if you follow the guidelines of the particular publisher [available in Writer's Market, or online at the publisher's web site], you raise the odds in your favor. Keep submitting! Don't submit the same item to several publishers at once. Publishers tend to know each other, and you can easily get blacklisted. Read up, and you will be ahead of most new writers out there competing for the few slots available. Even established writers have to compete, because the editor is focused on his or her idea of what the market is doing, and how your book might fit. The editor has to fight for his choice of writers. Make your manuscript worth fighting for, and follow the advice given in Writer's Market and Writer's Digest at http://www.writersdigest.com; but don't be discouraged when you get rejection slips. File them away as proof that you are a fighting writer, and be proud of them. Keep submitting. Keep writing; your chances are much better when you submit one item to one publisher at a time, carefully noting where that item has been; then send other items out the same way, and log where you sent them. The more manuscripts you can have out at one time, the greater your chances. Never put excerpts on the Internet of your writing that you are sending to a publisher; make sure it's never been publicly posted, because this affects your copyright.
Don't give up. When your manuscript comes back with a rejection slip, go over it and check for grammatical errors, spelling, and things that don't make sense to the central idea or plot. But, don't take every suggestion on how to improve it to heart; if your friends read it and the same thing comes up with several of them, you might consider changing whatever. If you don't have readers, don't worry; many authors got published without joining a critique group. If you try a critique group and like it, that's fine; but if you join one and your self-esteem hits the floor, get out! Write for you, not for whatever audience out there. Trying to identify your market is very, very difficult, and your editor will help you with that, once your manuscript is accepted. Most editors don't know exactly why they reject a manuscript, and it may have nothing to do with your talent, but rather what he or she bought this year, or his or her perception of market, which is incredibly complicated. Just keep submitting. Only change your past work if you feel your writing has changed for the better, and save those past versions. An editor will often ask if you have something else. Keep writing so you'll have that 'something else'.
Read a lot, and notice things like where the dialogue fits in, how it's formatted, etc. Do you like the characters? The plot? How about the descriptions of people and places? Writing that you like can influence yours, or give you ideas, but don't alter your writer's voice to match someone else's. You have to retain the you in your writing. Each writer has a voice. You have to write enough to discover it.
Never give up. Raise your writer's voice to the world, and join in the beautiful harmonies!