Make sure you've installed entrance reducers and mouse guards. Also, use duct tape to seal up any holes or gaps that might let too much cold wind blow into the hive. Make sure the hives have an upper entrance, both for ventilation and to allow bees easier access to outside when we get flying days in late Winter/early Spring. If you wrap your hives, wait to do this until the weather forecast doesn't show promise of any long spells of warm weather (usually after Thanksgiving).
Add a 1-1.5" inch piece of foam insulation board (blue board or pink board) between the inner and outer cover at the top of the hive. This reduces condensation build up above the cluster of bees on the inside of the hive. If not done, condensation can build up on the underside of the inner cover and drip down on the cluster of bees. Wet bees during the Winter equals dead bees.
Reduce cold wind exposure by placing windbreaks on the W and N sides of the hives, or wrap them with roofing felt (remember to cut holes for the bottom and top entrances).
Following these basics won't guarantee Winter survival, but it will help to put the odds in the bees favor.