You may already know this but for an engine to start and operate properly it needs the right amount of fuel, the right amount of air, compression and spark at the right time. From my experience most no-start conditions are fuel related and usually gasoline from last year was the culprit. You need to perform a few diagnostic checks to determine what part of the equation is missing. Spray a little carburetor cleaner in the carburetor and try to start the engine. If the engine runs for a second or two and then dies after spraying a little carburetor cleaner in the carburetor, this indicates that the engine is not getting fuel. One of the most likely reasons the engine is not getting fuel is that the carburetor jets are plugged and the entire carburetor needs to be cleaned.
Check for spark using an approved spark checker. Does the coil produce a blue spark?
After cranking the engine several times, is the new spark plug wet with fuel? If so, then the engine is getting fuel but no spark.
Is the air filter completely plugged with debris?
Check the above, report back with your findings and we'll go from there.
Good luck