Buy good shoes with nice grip, do some exercise and take thermals but only wear them at night...take good jackets, pack minimum but essential items... Dont use more phone, embrace the beauty of magnificent and the most beautiful mountains
I have been there around and of October couple of years back and it was already pretty cold. And the trail gets pretty slippery if there is fresh snowfall so I would advice you get an idea about the weather before your trip. happy trekking! 🙂
Do check my post For kheerganga travel. I travelled around June month which was preety favourable. Dec will be also good since it won't snow so early. It will be super cold and no rains. so you can travel . Until and unless by any chance, roads are blocked by snow.