Put some fuel stabilizer in the tank. Gas will only stay fresh for about one month. One good product is called "Sta-bil." And another tip, take out the spark plug, and pour in one tablespoon of your pre-mix oil into the cylinder. Then just hand crank the bike over once or twice, this will coat the piston, rings, and cylinder walls.
I put fuel stabilizer in and start up the bike and let it run for a a few seconds then i turn it off shut the petcock and drain the carberator bown via the main jet access plug. That way you don't have to worry about the carb. On the speed channel they were talking about winterizing your motorcycle and they said after 30 days gasoline starts to form a hard varnish and thats what clogs carbs.(I just found that interesting, doesn't take much to keep me interested.)
Or you could just ride it in the winter and not have to worry about it!