When you are planting a tree, spraying WD-40 on your shovel will make it slide into the soil much easier, making it smoother to dig through compacted dirt or heavy clay.
Wait a minute or two for the spray to dry, then proceed with your task. WD-40's lubricating nature will reduce friction, making it easier to get through
Since WD-40 is also a water displacer, it will help the shovel stay dry and easily part the wet dirt. Since the clumps won't stick to the metal, the shovel will be left cleaner.