I'd say start with the basics. Make sure battery terminals are not corroded/broken and tight. Check air box for any mouse nests.
Cars/bikes that sit for awhile always get these. Change oil,filter, and fuel filter. Change the plugs. Change any fuel pump/fuel injector fuses. Check/replace fuel relays. (all the inexpensive stuff). Do you have a test light? I'd start checking to see where i have power and where i don't. Check to see if power is going to the relay, then if it's going to the pump.