Unused oil is best as it keeps the petroleum esters from etching the metal surfaces while it sits. Also, it's helpful to fill the tank with stabilized fuel, turn off the petcock, drain the float bowls, run the engine until it's dry; pull the battery out of the frame and put it on a trickle charger like a Battery Tender. If you can leave the bike on a lift to take the weight off the tire, even better. And cover it.
