I want to travel to Tibet in early December and ask my relatives for advice.

The way to enter Tibet is by plane, train, car, bicycle and hiking. Consumption depends on the individual, off-season, but because it is winter, some places are not convenient to go. I suggest you pay attention to some people who travel in Tibet on Weibo and get to know them better. I met a man who has been to Tibet many times. He said that he can go in any season. But you have to have an idea of the weather conditions you may encounter. If you really can't, just sunbathe in Lhasa.