Observing at the Northern Hemisphere started as early as December 6, when one meteor every hour or so could be visible. During the next week, rates increase until a peak of 50-80 meteors per hour is attained on the night of December 12/13. By December 18 meteor shower disappears in the vast space.
Luckily, the Moon will be absent when the Geminids are at their peak on the evening of December 12/13.
The following charts will help you find Geminids from both hemispheres: