Hatsumode is the traditional visit to a Temple or Shrine at New Year.
here's a good video about Hatsumode. The title of which translates as something like "Middle-aged lady in a mini-skirt goes to Hatsumode"
[youtube:http://www.youtube.com/watch?v=tdhWda1KcMw]
The best time to go is 12 midnight on New Year's eve. Take a warm coat and a flask of hot tea (or something stronger) with you. Best shrine (which usual means most crowded) to go to is probably Meiji Jingu near Harajuku.