take the battery out and put is in a warm place on battery-tender plus 1.25 amp automatic shut off charge, don't allow the battery to freeze up, and yes leave the rad fluid in, it won't freeze as long as it is not pure antifreeze, the best is 50/50 mix , without water mix antifreeze will actually freeze up and crack that rad, and expose to cold wind an rad might crack, so keep your bike out of the wind, top up the tire pressure and do it again in the spring, lube your cables if you have any and watch out for mice if you're storing the bike in a shed, they will make a nest just about anywhere on your bike, and don't be tempted to start up your bike during mid-winter to hear the pipes, that can cause the engine to heat then cool causing condensation moisture in the crankcase, (read rust), and don't cover the bike in a tarp or plastic or sheet cause that traps the moisture, (read again rust), leave the bike fully exposed without a cover sheet, see you on the road in the spring