Actually...it's all about the publisher's submission guidelines. The majority of publishers have a submissions guidelines page that explains in detail what they expect. It pays to read them carefully.
1) Do they or don't they accept non-agent represented submissions? Many do not!
2) Are they currently accepting submissions? This can depend on season, how far behind they are and lots of other factors.
3) Does your work fit their needs? It pays to look at who they have published in the past. If you are not sure, hit a book store and look at authors with their publishing label.
4) How do you submit? Some accept email, but very few. Most still prefer snail mail.
5) What form and quantity. Most publishers ask that you send a query letter and Self Addressed Stamped Envelope (SASE), before you send any material. Some will request both the query and a couple of select chapters. Still others, demand a query, synopsis, and the first 100 pages. Anyway you look at it, the cover letter is do or die. They get thousands of them. If yours has errors, is not right on point, or doesn’t grab them out of the gate, it will be hard to get past that step.
6) Be very aware! Many publishers will not accept material from you in a multiple submission scenario. I mean, you can't send it to them if you have already sent it to others at the same time. They want you to send them the manuscript and wait as long as six months for them to say yes or no. If you do decide to send multiple submissions, it is strongly recommended that you tell them that this is the case. Frankly, the level of arrogance you can find in the publishing world is hard to imagine. Just don’t take them personally. There are also some really great people out there.
I would suggest that you buy a copy of Writer's Market. It will give you a huge list of publishers and what, how, and when they will accept submissions. Patience is required and the printing, postage, etc., can get expensive.
FOLLOW THEIR DIRECTIONS. If you don’t, most publishers will write you off permanently. They have very long memories.
Hope this helps.
"Without goals and dedication, dreams are simply fleeting images that quickly fade when we open our eyes." Author: Practically Invisible. Columnist for Writer's Beat E-zine. Guest Columnist, The Orange County Register, CRN and Government Var Magazines. Political strategist and Chairman, OC, AEA Government Affairs Committee.