How do you decide which data goes in the body of a Task 1 report?

When a chart has far more numbers than I can mention, I struggle with the grouping. Do you pick the highest and lowest, or group by a similar trend? I was thinking of testing each choice: cover one figure and see whether the overall story still makes sense without it. If it does, maybe it wasn't needed. Not sure that's a fair test though, since some numbers support the overview even when they look minor.