For some context, I have run Call of Cthulhu 7e in the past a few times for just one shots. It was a bit rules hand wavy, but it was really to see if my friend group would be interested in playing the system. After a few Halloween one shots, they've shown clear interest in trying a full campaign of the system.

The issue I'm running into is I have a hard time understanding how to run a long term campaign. I know the game can be very brutal with difficulty, and sometimes plot lines can become a touch confusing given the nature of cosmic horror. I would like to run a story of my own creation, and cosmic horror writing is something I actually have a touch of experience in.

I'm looking for tips on how to write something that can maintain a good length of the campaign, be fair while still being challenging to the players to emphasize that horror component, and just any tips or tricks that GMs have running the game.

Anything will be super helpful, but know that I am set on writing my own story. I know running a premade campaign will probably be easier, but I like to put a lot of effort into my campaigns so that I make a hell of an experience for me and my friends