Sharpen the blade before and midway though the lawn cutting season. A sharpened blade shreds the grass much finer and prevents tearing of the top of the grass as the blade passes over it.
Cut the grass more often than with a regular mower. Grass pieces that are 1 inch or shorter shred better and faster than longer pieces.
Set the height of your mower for the optimum shredding. This takes experimentation, as each lawn interacts with different mowers in different ways.
Avoid overly-wet grass as it clumps together under the mower deck and on the lawn. Grass with a light morning dew on it rapidly decomposes in warm weather.
Resharpen the blade before shredding leaves. The material that leaves are made from is tough and rapidly dulls a blade.
Shred the leaves before they become too thick on the ground. Some mowers can handle 4 to 5 inches of leaves while others choke on 1 to 2 inches. Shred slowly and make multiple passes to ensure the leaves are all finely ground.