It depends on the format in which your book will be published.
For hardcover novels, the average royalty runs from 10--12% of the cover price. For trade and mass market paperbacks royalties average 6--8% of the cover price. Also, as the number of books sold increases, there is often in increase in the royalty. For example, for a mass market paperback the royalty might be 7% of the cover price for the first 50,000 copies and 8% thereafter.
Books sold in an electronic format before being printed tend to have little or no advance and a high royalty. I've heard authors are paid 25--33% of the retail price for e-published books. The 'catch' of course, is that most of these books sell far fewer copies because they are not available in traditional retail stores.
Most first time novelists do not earn royalties above their advance, so if you are not being offered an advance, I'd advise you to consider looking for a different publisher.
Best of luck in your writing and publishing endeavors.