The best models are the ones a founder can defend line by line in front of a stakeholder, not the ones with the most tabs.
A model with fifteen interconnected tabs and hidden hardcodes might look impressive, but it fails the moment someone asks 'what happens if your CAC doubles?' and the founder has to go hunting through formulas to find out.
A useful model is driver-based: every assumption lives in one place, every formula references it rather than repeating it, and changing one number should ripple correctly through the whole model without breaking anything downstream.
Runway planning deserves particular care. It's not just 'cash divided by burn' — it should account for seasonality, planned hires, and the timing of large one-off costs. A runway number that ignores the hiring plan already baked into the budget isn't a real runway number.
Finally, a model should have a range, not a single point estimate. Base, upside, and downside cases built on the same structure let a founder answer 'what if' questions in real time instead of promising to follow up later.