Use the information gap
The official description says the navigator can see the stage map while the driver has no HUD. Focus on the next turn and visible hazards, and speak early enough for the driver to react.
Call one thing at a time
Use brief, consistent direction and hazard calls. Avoid long explanations during a difficult section; discuss what went wrong after the run instead. The listing does not specify an in-game pace-note system.
Verify the current interface
Map symbols and stage details are not described on the public listing. Inspect the current map and any in-game legend before treating a symbol as a confirmed hazard or route instruction.