Tax treatment for book income

You will be required to show it as business income as you are earning income from your own skills.
you shall all get deductions that ate required to be incurred to earn the income. you need to have all the invoices in place to provide proof for claiming deduction.
Advertisement income can either be shown ad business income or as income from other sources.

Thank u for your feedback. I was under the impression that royalty on books can be declared as Other income in IT returns. And only if book authors seek upto Rs.3 lakh income tax deduction u/s 80QQB, they should declare royalty as business income ?

Please follow the details how the same will be treated:
1. In case you are required file your returns.
The querißt has not mentioned any values r
2.In case there are some details yo be followed as per Sec 44 AA. Maintainance of books of accounts and getting the accounts audited is not mandatory. However,he may maintain such books.
3. modus of operandi of annual accounts getting audited and filing returns is enumerated brlow:
a)deduction is allowable from Sec 80C to Sec 80U

Thanks for ur feedback.To clarify, book writing is not my regular profession, just freelance work. 

If there’s no business and expected income from book sale is very modest, is it necessary to show as income from business and profession? 
Can someone come across instances  in which such modest book sale income can simply be declared as “Other income” in ITR1?

Normally incomes are classified into other incomes which do fall under any of the other heads.
in your case incomes is generated by applying your professional skills even though it's modest.
however whatever source you show, it needs to be substantiated to the satisfaction of Income Tax officer.

If showing as business income is the  option being suggested, then May as well get into the trouble of applying for GST number, correct?

So, this option means complicating the tax returns (which is good news for CA firm handling returns) as other income is also there and business income with GST benefits too?
Although read somewhere that mandatory registering for GST is not required even for established authors 

If your sales are exceeding the prescribes limit of 40lacs p a. then gst is required.
also if you selling to registeted persons and they want to claim tax credit then also you need to register for gst