When I started writing, my CPA took a number of advanced courses on entertainment accounting so he could continue to do our taxes. So, I trust his judgment. Here's what happened last year:
Writing income was categorized as a "business", and the income and expenses appeared on Schedule C, "Profit or Loss from Business."
Income is Gross Income of a business, (rather than Royalties which appears on Item 17 on the main form 1040, under "Rental real estate, royalties, partnerships, S corporations, trusts, etc.", which would be listed on Schedule E. According to Schedule E, Royalties are things like gas/oil leases and such.)
Expenses on Schedule C are broken down into sections like Advertising, Commissions, Car/truck expense, depreciation, contract labor, insurance (not health), legal and professional services and office expense.)
My agent fell under "commissions"
My copies, ARCs for review, website maintenance, bookmarks and postcards fell under "advertising"
Postage, dues and subscriptions, and office supplies fell under "Office expense"
My entertainment attorney fell under "Professional Services" and I presume that either this is where a professional editor would show up, or as contract labor. Definitely a question for the CPA.
And my convention appearances and booksigning expenses showed up under "Travel, meals and entertainment."
I paid income tax, social security tax, (no state income tax in Texas, but probably that would be an issue elsewhere), medicare contribution and self-employment tax. Of course, last year I posted a negative number due to my promotion expense, but I'm planning that this year the numbers will reverse!
Hope that helps!