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.
Keep the center clear and calculate every segment against the same whole.
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 omit values because of the center hole or distort proportions with excessive segment gaps.