First check for a spark, then follow my advice above "check compression, then squirt a little gas from a blowlamp down the air intake, because this disperses without "wetting" the plug if it is giving too rich a mixture, and as it disperses, there will be one point where the air/fuel/gas mix is just right and the engine will fire, unless something else is wrong with it."

After being stood, an electrical wire or component may have corroded, hence the check for a spark, the carb may have congealed fuel, water or dirt settled in it, clean it out properly. Or a valve may have stuck, the compression test will show that.