I can only tell you what I know from the standpoint of publishing traditionally through one of the top 2 publishers in the world. Trust me = I know my stuff. I do this for a living.
Let me just give you a general answer in dollars and cents. It's complicated so stay with me.
A smart author invests in an editor before the book goes through the query stage. At that point, you can retain rights to any and all edits made in your book. A good editor knows how to take a good novel and turn it into exactly what a publisher is looking for. Expect to pay 5-10 dollars per page based on 250 words per page, but they are worth it. An editor's margin notes can really help you get your novel in great shape. They have been down the road before. They know their stuff. They also know agents and may be able to recommend you to one. But it costs money up front.
If a publisher decides they are interested, they sign a standard book contract with you. That calls for you to receive 10% royalties from the sales of your book. 15% of your 10% goes to your agent for negotiating the deal.
The price of your book is set at 6 times the cost of production. Generally these days, with a hardcover book that comes to about $24.99. That means that for every book you sell, your share is $2.49 less 15% for your agent or roughly $2.12 BEFORE TAXES.
Today, it is common for a first print run of a newcomer's book to be about 15,000 books. Much less isn't profitable to print. Therefore if you sell all 15,000 of your books, you stand to make $31,800. If your agent has done their job, they have gotten you an advance of 50% of your royalties or $15,900 - of course that is taxable income.
That means that when your book sells 7,501 copies, you start earning your additional $2.12 per book. But publishers aren't fools, they are businessmen. If your book does not sell 7.500 copies, you will likely be asked to return any portion of that $15,900 that is owed to them.
If you are smart, you take that $15,900 and plow it into marketing and promoting your book so that you sell the rest of the first print run and get the publisher to do a second or even third run - which your agent will negotiate at higher royalty rates and a bigger advance. It takes money to make money. If you paid for an editor, you are still running behind at this point. You NEED to remember Uncle Jim's rule of publishing. Money should start flowing toward the author not away from him as it does in self publishing.
Of course, this means your royalties end up being nothing, but you are investing in your future as a novelist. Often, if you are willing to invest, you can get your publisher to contribute a similar amount. Again, this is if your agent is on the ball.
If your books do not sell and end up on the bargain tables we all see at the major book stores and I walk in and buy your book for the reduced price of 7.00, you make ZERO. Nothing.
If your publisher negotiates with one of the large wholesale clubs like Costco to sell your book for half price - or approximately $16.49 each, you take the hit. Your 10% is based on that number. Of course, you will likely sell more copies in those clubs, so it is advantageous. A good agent will work on book club deals for you. Also, when you walk into a major bookstore these days and see books on displays at the counter and near the front of the door, that costs money. It is paid advertising. Sometimes as much a dollar a book to get placed up front. But that is where people will see you. So your marketing plan may involve getting your books placed on those tables for a day or two. YOU the author pay most of that cost. Publishers invest very little in marketing for novice authors. Brown Little got burned paying 50 million dollars to advertise The Historian for Elizabeth Kostova and now it is available on bargain shelves for 5 bucks. They save their big advertising dollars for the big time authors.
You do not get rich on a first novel. It is very rare. If any one asks you to pay money to look at your book, they are a self publisher and you should run fast. The only things your agent may charge you for are the standard 15% commission plus incidentals like printing costs of copies they have to send to publishers, postage, long distance calls etc.
The 90% left goes to the printer, and the publisher. They are the ones speculating on you and that is how it works. They have to pay editorial staff, attorneys, and many other people who will be there actually "working" for your book. They do earn their share. Believe it or not.
The big money comes if your book does well enough in hardcover to warrant paperback rights being sold. Stephen King got a 2500 dollar advance for Carrie from Doubleday. Doubleday in turn sold the paperback rights for 400 thousand dollars, of which Mr. King received 200 thousand. It sounds great, but it's still not a terribly huge sum considering what you have to invest to make your book successful enough to get a big paperback advance. You will find you make next to nothing on foreign rights. In some cases - absolutely zero, but it is cool to see your book in other languages so some authors do it anyway.
Also NEVER tell a publisher you are writing a series. They will be very hesitant to even look at it. They will never enter into a multi book deal with a new author. What if the first books tanks and they still owe you two more? It works the other way, too. If the first one does great, you have more to negotiate the second and subsequent sales with. But make sure your first book can stand alone. There may not be another.
It's all about building a reputation over time as a reliable and steady seller whose books get better with each new one and climb the charts higher and faster. That gives your agent more room to negotiate and more leverage for your next book and the one after that.
And by the way, only 5% of authors make a living at it. The rest work. You can look up an author by the name of Glen Cook. Writes great Sci Fi and satire. I love his Garrett series books. He has a huge underground following and until his publisher started rereleasing them recently, you had to pay 40 - 50 bucks for a raggedy paperback online. He wrote for years at night while working days at the GM Light Truck Assembly Line. If you have a GM truck, he might have built it. And he wrote a ton of excellent books while he worked there.
If you go to my profile you will find I star all the Q and A on publishing and writing. Read through them and print out ones you think will help you. Many successful and legit authors post here and do a lot to help novices learn. Pax-C
Author of 5 novels, ghostwriter for several sports stars, unabridged editor, book doctor, CW teacher from ages 6 - adult and beyond.