Basic rules
Do
Use it for nonnegative parts of the same whole and identify that whole and its time period.
Provide names, values and proportions, and choose a bar chart when small differences matter.
Associate labels and leader lines with the correct slice and use a legend on narrow screens when needed.
Don't
Do not combine overlapping categories or values belonging to different wholes in one pie.
Do not create excessive tiny slices or distort angles and areas with 3D or tilt effects.
Do not force values inside tiny slices and overlap labels.