Agree the commercial signal first
Sales, qualified leads, bookings, average order value, repeat purchase and cost per acquisition: pick the two or three the business genuinely runs on and write them down before the first asset is produced.
Everything else becomes diagnostic detail rather than the headline.
Separate demand creation from demand capture
Brand, social and creator work mostly create demand. Search, retargeting and the site mostly capture it. Judging one with the other's metrics reliably leads to cutting the thing that was working.
Report in decisions, not dashboards
A useful report ends with what will change next month and why. If nothing changes as a result of the numbers, the measurement is decoration.
Measure what you would act on, then actually act on it.