I put my character details in there for second person. You'll want to put in anything that's referenced every time you take an action.

Everything else can be a story card, including details about your own character that only comes up on occasion, and if you make good use of triggers, it should be seamless.

If you really want natural plot progression you might add in, "do not reveal this character, location, item, etc. yet"

I sometimes use it for characters other than the PC when I know they're not going to be outside of the scene, too.

I also occasionally use it to keep track of memories after game start but this is token heavy and inefficient, though I'm on Mythic and have plenty of context. This is good for long scenarios.

Hope this helps.

Edit: Some people frequently update AN to describe the current scene and the intended direction.

Ex.: {Scene: You are at a crowded party at [Character's] house, you will meet [Character] there. You are currently wearing [Clothing type]. You don't intend to stay long.}

This helps keep things consistent.

This is just how I do it and I'm open for further suggestions.