The first step is to get all the tools and equipment you'll need. These include a power drill, work gloves, a blade sharpening kit, a torque wrench (or a socket wrench in a pinch) and a wooden block. Consider having a rubber mallet on hand, too. Other items include a plastic drip tray, motor oil and a container for waste oil.
First try blowing dirt and old grass clippings out with the leaf blower. If that doesn't work, scrape debris away with a putty knife. The last resort is to spray it with a garden hose. Unless your mower has a special washout hose connector, you risk damaging the engine, wiring and other sensitive parts.