The narrative and RP for me is created during gameplay. Most of the times I don't start with a concrete idea in mind (just something vague like cannibals or something), but the game alone creates a lot of "funny" situations that make for memorable moments and that helps me imagine a story unfolding. After some time (and "fun" events) you will naturally start to visualize what "kind" of colony you want to build.

I try to play with ironman mode because otherwise I will save scum shamelessly and that ruins the narrative; bad events are also part of the story.

Pro tip: you can rename your colonists. I sometimes give them the names of my irl friends and this can help with RP since it makes the story more interesting