Check the safety key and make sure it is fully inserted. The unit does not start without the safety key being present.
Make sure the choke is off. Move the choke control to the "off" position.
Check the fuel tank to ensure there is an adequate fuel supply. If the fuel is old or dirty, you may need to drain the tank and fill it with fresh fuel.
Check the spark plug wire to see if it is secured to the spark plug. Pull the plug wire off with your fingers and push it back on tightly.
Replace the spark plug. Remove the plug wire by pulling it off with your fingers. Remove the spark plug with a socket wrench. Install a new spark plug with a socket wrench and push the plug wire on tightly with your fingers.