Wont firi over been sitting for a while
The following applies to pretty much any carbureted engine.
You need three things for an internal combustion engine: Fuel, Spark, and Air.
The first place I'd start is with the spark plug.
Remove the plug. With the plug wire attached to the plug, ground the electrode (threaded part) against the metal frame and crank the engine again. Check to see if there's a spark between the electrodes. If there is, then you've established spark - for that cylinder and only that cylinder. If you have spark in all cylinders, next thing I'd check is fuel.
I would start at the fuel inlet of the carb. Pull off the fuel line and make sure fuel can get there from the tank. If not, you have a plugged filter or debris in the tank that's preventing the fuel from reaching the carb. Clear the obstruction and try starting.
Still won't start? There is the possibility that gas in the carb has dried out. That can plug ports, keep the float from working, etc. Best fix is a carb cleanout.
On some bikes, you can check to see if the float is working. There is sometimes a drain valve in the sediment bowl (on the bottom of the carb). Open the drain and see if gas comes out. If it doesn't then there is no gas in the carb. If no gas comes out, then it's likely that your float is stuck.
If you don't have a drain valve, on some carbs, there is a "nut" on the bottom of the sediment bolt. It's actually a bolt that holds the sediment bowl to the carb. Loosen the bolt until your bowl is free to move. If no gas comes out between the bowl and the carb, your float is stuck. If it does come out, then it could be the needle that meters gas to your engine. Work the throttle a few times and then try again. With the gas in the bowl, working the throttle moves the needle in and out and can clear out enough "varnish" to let gas get into the cylinder.
Again, try starting it. Still no joy, pull the plug and see if it's wet. If it's wet, then it has been getting gas - too much, in fact, but that's because it hasn't been firing. You're back to two issues:
Either the needle isn't closing and too much gas is getting into the cylinder or you don't have spark. If it's the first, then you need to pull the carb for that cylinder, clean it out and re-install. If it's the second, you have an intermittent wiring problem which is going to be a lot of fun to find.