Lawn mower maintenance is a very important ingredient to the welfare of your lawn. Making sure that the blade on your mower is sharp ensures that the blade actually cuts the grass instead of ripping and pulling the grass. Your grass will be much greener and healthier.
Remove the lawn mower blade using an adjustable wrench to remove the bolt from the center of the blade.
Pull the blade off and clamp it in a bench vise.
Check the blade edges for small nicks and remove them using a flat medium file.
Follow the original bevel of the blade and move the file toward the cutting edge with smooth, even strokes. If you are comfortable using a bench grinder or an angle grinder this is also an acceptable way to sharpen the blade. Just make sure that you do not force the blade into the grinder, this will heat the blade and cause the metal of the blade to lose its hardness.
Make sure that you make the same number of strokes on each edge. If you take more metal off of one side than the other, the blade will be out of balance. This will make the lawn mower vibrate, causing serious damage to the engine.
Make sure the blade is balanced by placing the blade on a dowel or the end of a screwdriver. If one side points up, sharpen the other side until the blade lies flat.