Yes it happens quite a bit these days. A relationship ends and people go their separate ways. The house is up for sale and so is someone's heart!
In the past eight years, I have done alot of these types of jobs. Its sensitive and quite tough at times. Besides dealing with the end of era, you have to make alot of decisions. Respect and kindness are the key to getting through this project.
First off, get packing supplies. I love my banana boxes from the grocery store. They are the perfect size for books, and smaller items. Any storage place will sell you boxes and tape. Consider if you will need wardrobe boxes or speciality boxes for art or fragile items.
Create a staging area for each person. If the home is on the market, then consider using an area of the basement to stage the boxes until they can be moved out.
Take one room at a time. If items clearly belong to one person, pack them up immediately. Clearly label each box as to who it belongs. If a decision needs to be made on something, move it to a corner till they can be decided upon. I like to use postit notes to put above different areas of staging.
The goal is to finish and shut down one room at a time. Its a good time to purge as well. Why move things you don't need or want to a new home? Trash or shopping bags can be used for loading up donations.
Set a daily goals for yourself. You will be amazed on how quick it goes!