Basic rules
Do
State each dimension, direction and scale and keep axis order consistent across comparisons.
Explain normalization when comparing different units and provide the original values.
Limit the number of compared series and distinguish overlaps with lines, legends and transparency.
Don't
Do not interpret polygon area as a total score or reorder axes to make performance look larger.
Do not force a radar chart when there are too many dimensions or overlapping labels.
Do not let fills obscure another series or use different scales for each series.