From the DMs Guild page:
Fleshing Out Curse of Strahd is a series of expansions and elaborations to the core Curse of Strahd campaign. The full series is a DM tool that adds depth to various NPCs, streamlines confusing plot lines, fills in plot holes, and alleviates some of the stress associated with TPK inducing encounters throughout the campaign.
Within Chapter 1: Prepping the Adventure, you'll find the following:
Barovia's Background. Information regarding the cosmology and background of the module, including the Domains of Dread, Dark Powers, and the setting's timeline.
Adventure Flowchart. A more in-depth adventure overview and leveling guide for aspiring DMs.
Campaign Specific Tips and Tricks. Are there common pitfalls DMs should avoid in this specific campaign?
Advice to Get Started. What should DMs prep first? What areas and characters are most important?
Incorporating Your PCs. How can DMs incorporate PC backstories into this campaign to make it more engaging narratively?
Expanding the Setting. What exactly do Barovians eat? What does their culture include beyond fear? And, most importantly, how long exactly does it take for parties to get from Point A to Point B?
Including the Fanes. The Fanes of Barovia are mystical nature goddesses of the Barovian valley from past dnd editions. Let's resurrect them to add depth to the 5e campaign!
Dealing with PC Lycanthropes. So your party has been infected with lycanthropy? Let's make this interesting!
Amended Magic Items: A few additions and edits to the magic items in the module.