Again and again the question comes up: "I have a manuscript. How do I send it, with a letter to the editor, so that the publisher will actually read it?"
Others can give more extended advice than I, but it's really quite simple.
Try and imagine yourself in an editor's place, receiving a manuscript from an unknown writer. Then use your common sense:
"If I were the editor,what kind of manuscript submission and accompanying letter would make me want to read the manuscript?"
Yes, you need to know the formalities (correct line spacing on a document, begin your letter with "Dear Mr/Mrs." instead of "Yo", locate the correct address of the editor you wish to contact, etc.)... but more than that, you need proper attitude.
1. Be polite. It won't kill you, and it certainly won't kill the editor.
2. Be honest. If you haven't finished writing your book, then you shouldn't send three chapters to a publisher and pretend the rest is already finished. Don't try to be something you're not. They Will Find Out.
3. Be aware of the competition. The bigger the publishing house is, the more manuscripts will flood it every day of the week, every year.
Think of it as the competition among astronauts in training: the seats on a spaceship are SO few, the candidates are SO dedicated, SO 100% focused on success, the odds are naturally stacked against you.
In other words, it doesn't help to write a desperate plea: "Pl-pl-pl-PLEEEASE publish my book! I'll do anything!!" Prepare to be rejected... but don't let that make you cynical, either: "I'm sending you this manuscript even though I know you'll reject it, you money-grubbing bastards."
4. Do your research. There's no point in me listing all known publishers here; the publishing landscape is shifting fast. Make a Web-search. Find the small-press houses that operate in your area/country. (If they haven't at least got a webpage, they're not worth writing to.)
5. Be a cheapskate. Publishers are mostly a conservative bunch. They may demand that you send a printed, double-spaced manuscript, and a stamped return envelope... which means postage and paper expenses for you.
DON'T DO IT. Ignore those publishers until they have learned to accept electronic submissions.
6. Be lucky. I hate to admit it, but there is an element of blind chance. No matter how good you are, there are too many unforeseen circumstances and whims of publishers (not to mention all that competition).
Some people say that the bookstore market is glutted with too many titles anyway. This may or may not be true (at least for Western markets). Are you sure you want to contact a publisher?
7. Fail, then try again. So what if you were rejected? Find another publisher, and try again. If you're not a patient soul, this business may not be for you.