Remove the battery. If you can put it on a tender, fine. If not, it might be toast anyway after that time.
Drain the carb, totally, bowl especially.
Either fill the fuel tank lipping full, or drain it and slosh a coating of light oil inside, covering all surfaces.
Pour a thimble amount of oil inside the cylinder and put the old spark plug back in.
Overfill the crankcase with most any oil.
Lift the bike so that the tires are off the ground - block under the skidplate, etc.
Remove the chain and place it inside a bag with a liberal coating of oil. If you can't do that, just coat the hell out of it with a heavy oil like gear lube.
Clean the bike well and spray it down with something like WD40.
Keep it in a dry place and cover with a tarp.