Start with a playable milestone. Define the beginning, the actions available, the success or failure conditions, and the ending. Then list the systems required to make that experience work. Keep future possibilities in a separate backlog.
Write observable acceptance tasks
“Add saving” is broad. A clearer task describes what is saved, when it happens, how the player resumes, and what happens if the data is missing or incompatible. Similar detail helps with controls, menus, progression, and content tools.
Identify dependencies and supplied material. A character feature may require art, rigging, animation, sound, and interface changes. An apparently small request can touch several parts of the production.
Give new ideas a place to wait
Maintain a short list of additions with their purpose and likely impact. Review them at agreed milestones instead of inserting them into active work whenever they sound exciting. Necessary corrections can still happen, but the effect on time and scope should be explicit.
A stopping point is not a rejection of the larger vision. It gives the team a complete piece to test and improve. A small finished experience can provide better evidence for the next decision than a growing collection of unfinished systems that never meet in one reliable build.