Basic rules
Do
Compare category magnitudes on a common scale and start the value axis at zero when length encodes value.
State the unit and sort order and reserve enough room for category labels.
Use stacks for totals and composition and stack components in a consistent order.
Don't
Do not truncate the baseline to exaggerate differences or vary bar thickness between categories.
Do not rely only on color to identify categories or overlap an excessive number of bars.
Do not use it for precise comparison of middle segments with different baselines.