Check that the key is in the ignition and turned to the "On" position. If the key is in the "Stop" position, the ignition is disengaged.
Check that the choke is not in the "Off" position. Position the choke to the "On" position and press the primer to send fuel to the ignition.
Add fuel to the fuel tank. The snow thrower could be low on fuel at the end of one use and you may not have remembered to fill the tank prior to using the snow thrower again.
Inspect the spark plug connections and make sure that the plug wire isn't loose or disconnected.
Check the alignment of the skids and scrapers. Adjust them so that they are set at the same height on both sides of the snow thrower.
Check the air pressure tire in the tires on both sides of the snow thrower with a tire pressure gauge.
Add or remove air from the tires to make the tires equal in pressure so that the snow thrower is level. Take care not to exceed the maximum air pressure of the tires.