I Just Started a Side Business, What Do I Need to Prepare for Tax Season?

At the beginning of this year I published my first novel on Amazon. It has barely sold any copies (less than 100), but it has sold. I intend to keep writing more books and eventually get many more sales (to the point of one day potentially being self employed). What steps should I be taking to prepare for tax season? How will this affect my taxes now as opposed to later? At what threshold (of sales/income) will this likely have a significant effect on my taxes? And how do I best set myself up so that when Tax Season comes around I don't suddenly owe a bunch of money?

Do book expenses, such as editors, qualify as work expenses, and if so how do I factor those into my taxes?

Thanks! Really appreciate this event!