Just few words to what I have learned on my own by trying to publish a book in the last 5 years (smart and geeky people would found this in 5 days on Internet, but people like me have to do it old school and to verify it and to waste time).
The first ones I call them fishing publishers are just fakes and if a publisher want you to pay a part of printing costs you will end up with 20.000 copies of your book few months later if you buy them in the end otherwise they will be burned.
Publishing your own book by you is also silly - since just to print it out and to have it in your home - who cares (or you write it for friends and you print like 20 copies) ;)
A real publisher will take all the risk, will pay everything, will have distributors and will make a lot of publicity for it, since he want to make the most of it. You as a writer will end up famous if your book is a best seller. For your first book a real and serious publisher will propose you 8% to 12% (if your book sells for 30 you will gain like 3 and the 27 goes to the publisher). If a publisher offers you 30% try to smell the shit, since it is not real. And if your book goes and sell very very very well, than for the next one you can ask for more and if there is any chance you become the next J. K. Rowling you can ask whatever you want or start your own publishing house. Good luck with that.
Big and serious publishers are not difficult to find (just take a look at already printed books in bookstores. If you have a book already written than this is the way to contact a publisher. If you just started and have just this idea do not bother - there are millions of ideas - your book has to be finished, but do not expect a LE (literary editor) to read your 600 pages just because you have send it to them, since they have every day thousand of pages coming in.
To make it simple:
1. Take a look what your publishing house is in (what king of "genre"). If you write a drama, do not expect a publishing house that publishes mostly crimes and action to take even a look at your book.
2. Try to contact the publishing house, ask for a LE and ask them if you can send them a description and an extract of your book. Ask for his name and hopefully he might agree.
3. If he agrees or if you just send it to the publishing house than this is the best way. Few words like dear "LE", here is a description and an extract from my book that has 654 pages for example and it is a "drama".
The description should never be longer than a page (and do not fool with different writing styles - use Courier or Arial and 12ft, since it is the quite easiest way for the LE to read it. Do not explain what you want to say, just give a short description of the whole story starting by what is the "genre".
Your extract should never bee more than around 30 pages (the introduction and one chapter your close friends and family might find very interesting, since you are not objective with yourself).
And you have to send also a prepaid reply envelope and if the LE think that your idea might be interesting you will get a letter or a call and they will ask you for the whole manuscript. And from that point on the real work starts, since they might ask you to rewrite some chapters, characters, scenes, to remove something, to develop more and so on and so on.
That is the whole secret behind publishing your book. The most import remains still what you write and never forget if your character knock a nail in a wall at the beginning of the story in the end he should put a painting on it or hang himself in the end but you must never forget the nail - if you get my point. And if you reread your book, do not bee afraid to remove stuff or to change it.
So here is one more in the sea of thousands of article like that one. Was it useful - I do not know but the photo up there I took of this amazing house inspired me to write something.
Cheers and good luck