People have different approaches, but most approaches have this in common: they facilitate organization, sorting, and coordinating your upload to ACX (or other platform). My approach is described below. It does not need to be your approach, but I do encourage you to adopt a convention that helps you improve efficiency and be consistent about it.
##.#.BookName.PassageName
By having the number at the beginning, I can more easily sort according to the order in which the audience will listen to the files. Also, I like the number at the front to line up with the chapter number - just personal preference.
Certain elements of the book should always sort at the top (opening credits, prologue, introduction, etc.) and other elements should always sort to the bottom (closing credits, epilogue, retail sample). For my naming convention, I use "00" to designate files that are at the top and "99" for files that are at the bottom.
Example:
00.0.MyBook.OpeningCredits
00.1.MyBook.Introduction
01.MyBook.Ch1
02.MyBook.Ch2
03.MyBook.Ch3
04.MyBook.Ch4
99.1.MyBook.Epilogue
99.2.MyBook.ClosingCredits
99.3.MyBook.RetailSample
Last Note