If you mean Cherry and Brian, it’s best to start at this post here: Cherry And Brian, Chapter 0: Cherry's Backstory (Star-The-Alicorn)
And you work your way up numerically. 1, then 2 and so on.
If you mean headcanons, those can be read in any order at all.
I also have a story I’m beginning but working on, called “Cirrus and Whiskey”.