The amount of money you get as an advance against future royalties is based upon your reputation as an expert, how well you write, and how much the Publisher expects to make from the sales of your book. A good agent can help you get a better deal, but your track record as a published author and expert in the field will be your biggest bats for hammering home a larger advance. Royalties Royalties are the percentage of the price of a book that you will be paid for writing the book. Let's do some quick math. Not bad money.
Publishers pay royalties two times a year.
Some authors prefer to take no advance against future royalties and want to be paid from book sale one. Get money up front. Make sure you're paid for the work you do. Other authors will actually lower their royalty percentage on the back end in order to get more advance money up front. I come from the theatre where no back end money is guaranteed, so I try to get as much money up front as possible because that is dough you can bank on immediately.