a few other things.. turn ON the ignition switch .. and set the kill switch to RUN.. everyone (me) forgets once in a while..
Insects and rodents like to build nests in various parts of bikes.. and some vermin chew wires .. some builds nests or hives in the air intake box.
make sure there's plenty of fuel in the tank. If it started and ran recently but then wouldnt start, remove the carb intake hose and drain some fuel into a container.. if it doesn't flow smooth and steady clean the little filter in the petcock.
If it still doesnt flow go deeper, like remove the petcock and clean it's screen.
Another test for fuel entering the carb is it's float bowl's drain screw. It is accessed through the pedal sprocket and through a little hole in the engine's swingarm sheet metal. Get a falt screwdriver in there and loosen the drain screw. Fuel should continuously pour from the carb bowl's drain tube (Its end should be near the centerstand's spring). Get a bucket and rag so fuel isn't pouring onto the floor.