If you don't know where to start, figure out the answers to these three questions

Q1 What kind of book are you writing, or what kind of book do you want to write? i.e. what category or genre is it in, what does it aim to do, etc

Q2 Who are you writing the book for? i.e. what type of reader, or what target audience

Q3 What do you want in return for writing the book? i.e. do you want to make money, do you want people to appreciate your writing, do you want the validation of a publishing contract, do you want to reach a lot of people, or do you want other things


After figuring out the answers to these three questions, you should figure out your budget and timelines

1) What is your budget in terms of time and energy?
2) What is your budget in terms of money?
3) What are your timelines i.e. By when do you need to have your book written? By when do you want to have the book published? By when do you want to get the first X sales of your book?

If you don't figure out where you want to go, then, like Alice in Wonderland, you will end up somewhere you didn't really want to be

So, figure out where exactly you want to go, and then figure out exactly what resources and time and budget you have to get there