Formerly one of the tallest observation decks in Tokyo, the Tokyo Tower has recently been overshadowed by the Tokyo Skytree in height. In beauty, however, the Tokyo Tower is much better, especially when seen at night. As a broadcasting tower it legally has to be colored red/orange and white, which creates the vision of a punk Eiffel Tower in the night.
The best way to approach the tower at night is from the southeast. Travel to Daimon or Hamamatsucho rail stations, then head through Zoro-ji, a quiet Buddhist temple. Just follow the sidewalk to the tower--it's easy to see!--and take a quiet stroll to the base. Zoro-ji is typically deserted at night and no one will stop you from taking a moment of contemplation by one of the many statues.
Once in the tower you are able to go to the middle or top platforms to view the city. To be honest, if you're after a killer view, save your money for the SkyTree or go to Tokyo's city hall for a free observation deck. Tokyo Tower is best viewed from below against the Tokyo skyline.