Nevertheless, you can negotiate, so do it. How much, and in what form, the advance covers. When a publisher accepts a title for publication they work out how many copies they are likely to sell. Thus the payment of an advance is generally paid out over at least a year. The royalty you receive.
Royalty rates are, unfortunately, slipping.
Rising royalties basically give you a higher royalty once a certain number of books have been sold. VERY few authors sell world rights to their titles. Generally, you sign country by country. Thus there will be separate contracts for US rights, UK rights, German translation rights, French translation rights etc. These other countries don't automatically fall in line - you must sell your work to publishers in every country.