To start off you would want to check gas flow out of the line by taking it off and seeing if it makes a steady (if small) stream.
Then make sure your spark plug wire is on the plug right, some of them get bent up and make poor contact. Check the head nuts for tight. Then try starting it.
If no start or even trying to start, pull the plug and lay it on the head and walk the bike forward to turn it over and make a visible spark. If none, recheck your wiring connections and kill button.
Good luck to you.