Time series

The most common chart.

Getting it right

Keep time on the horizontal axis, use even intervals, and do not connect points across gaps in the data. Seasonal patterns need at least two cycles to be visible.

Index to a common starting point when comparing series of different sizes.
A moving average smooths noise and hides recent turning points.

Cherry-picked ranges

Start and end dates can make almost any trend appear. Show the longest sensible period, and be suspicious of unusual ranges in other people's charts.