Manuscript Preparation, Copyediting, and Proofreading
Q. How does one go about preparing an index? Any web page I can go to?
A. I typed “preparing an index Chicago” (without the quotation marks) into Google and found many sites that offer guidelines. Here are a couple, from University of Nebraska Press and Penn State University Press.
And of course chapter 16 in CMOS tells you all you need to know and more.