Remove blades and inspect the condition of the attaching hardware. It is a good idea to replace the hardware each time the blades are replaced.
When sharpening blades always wear safety glasses to prevent any debris from getting in the eye.
Sharpen the blade to match the original cutting edge. Do not go beyond the original edge and avoid grinding any notches into the blade. A notch in a blade can make them susceptible to breakage.
Always leave a 1/32" to 1/16" dull edge to prevent the cutting edge from chipping. It is not necessary to have a razor sharp blade. This will only decrease blade life.
Once the blade has been sharpened hang it on a nail or screw from the center mounting hole to balance the blade. If one side of the blade was damaged and more material was removed when sharpening this could create an imbalance and cause vibration. If the blade is balanced it should hang level on the nail. It may be necessary to remove more material from the heavy side to obtain proper balance.