Write Your World
I think the most compelling way a tabletop player can use their game to inform their writing is to literally write about the adventures in your world. Recap each session while it’s fresh in your mind. I tend to include any Natural 20’s or 1’s in my recap, as well as fun character moments and major plot points. This gives you an outline to work off of, where you can write scene by scene, arc by arc, or in any other way that makes sense.
Deep Dive Into the Psyche of Your Character
Maybe you’re the type of person who enjoys going really deep into the mind of a character. Have you ever thought of adding them into your campaign? Roleplaying a long-standing character can give you a deep look into the way they think and behave. Exploring your characters in this way can give you a real sense of how they approach problems in their own story worlds.
Explore How Things Could Have Gone
Playing a campaign that didn’t go the way you wanted it to? Maybe your DM/GM took the story in a direction you weren’t interested in, or maybe the party solved a problem in a way that you wouldn’t have done. You can use these scenarios to explore how you would have handled it by writing it out.