This is one chore/project that I actually enjoy, believe it or not. Recently, during Spring Cleaning, I re-organized the many closets in my house, so it's all fresh in my mind.
I haven't had to invest in closet organizers, but I know they are invaluable, depending on your particular situation.
I find it necessary to empty a closet, completely. A thorough cleaning from top to bottom, walls, shelves & floor, comes first.
The time-consuming part, comes next......but it usually ends up being fun and "enlightening." This is where I find all sorts of interesting things......that I may have been looking for, for months! The 3-pile system works well: Keep, Toss & re-locate. Being somewhat of a hoarder, it takes time to convince myself to simply throw away, totally old, worn-out, useless junk, that thus far, I was unable to toss.
Then comes the re-stacking, hanging & storing.....placing everything, ever so neatly and compactly as possible. After all the years of closet organizing, I believe I've got it down to a science and am always pleased with a job, well-done. A few years back, I decided to make a "list" of the closet contents and tape this to the wall or on a shelf, where I can easily see it, for future searching. This prevents having to "tear apart," all my hard work, while frantically looking for one little thing! Great feeling of accomplishment!