Perhaps one of the only useful pieces of advice I have is that if you see a chart that seems to show some absurd decline / spike in any metric in a short amount of time, it is very, very likely the result of data error or some kind of reclassification in the data series.

Doubly true if a) the chart relates to a complex and thorny topic with multivariate inputs and b) the direction of the chart plays to your confirmation bias.