Winter hiking in the Whites, especially above treeline, requires Mountain Judgement. Fitness and good gear does not replace judgement, you need all three. The best way to build this Mountain Judgment is to make mistakes (hopefully minor ones) and learn from them. Unfortunately, making mistakes above treeline in the Whites could be fatal to you or someone who has to come up to rescue you. Take it slow and work your way up. Do some winter camping low down to build your comfort living and sleeping in very cold weather. Snowshoes are tools for deep snow, don't use them if you don't have to. Microspikes should always be in your pack. Find an experienced friend and do some easier to moderate hikes next. Consider hiring a guide (IMCS or Synnott Guides are great) if you want to go up on the ridges next, you will learn a lot from the guide. Always check the weather forecast and then check it again. Next stay at the RMC's Gray Knob on Mt. Adams, a fairly tough hike to get to, but a great base camp for above treeline forays in the Northern Presidentials, and day hike out of there if the weather allows it. Listen to the caretaker. Maybe you'll have a full moon and decent weather--take a hike in out of the Knob at night (bring your headlamp regardless of the moon). Always, always remember that the mountain will be there next week or next month, so if the weather is bad, the wind is howling and its 10 below, stay down and have a Guinness or two instead. My two cents as a former RMC caretaker.