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.
Apply units consistently and keep value labels readable even on short bars.
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 inconsistent rounding between bars and labels or clip displayed values.