Basic rules
Do
Show magnitude and change along an ordered axis, with a clear baseline for the filled area.
Label axis units and aggregation intervals and distinguish missing data from actual zero.
Normalize each point to 100% and provide absolute totals separately.
Don't
Do not connect unordered categories or let overlapping areas completely obscure another series.
Do not fill gaps without explanation and imply continuous observation.
Do not imply equal totals merely because proportions match.