If you earn money working as a writer/author, the IRS recognizes you to be a small business owner or a self-employed individual. As such you will report your income on a Schedule C.
During the course of your work, you may receive royalty income from your publisher. Generally, these are reported to you on a 1099-MISC form. If you receive royalties that were reported to you on a 1099-MISC and you are currently working as a writer, you can report the royalties on the same Schedule C used to report your income as an author. Keep a copy of the 1099-MISC with your tax information in case the IRS requests further information.