How can I effectively trim cedar hedges to maintain their shape and health?

To effectively trim cedar hedges and maintain their shape and health, use sharp and clean pruning shears to make precise cuts. Trim the hedges in a slight tapering shape to allow sunlight to reach all parts of the plant. Avoid cutting into old wood and aim to remove only about 20 of the foliage each time to prevent stress on the plant. Regularly inspect the hedges for pests and diseases, and remove any damaged or diseased branches promptly.