WHERE: The above simulated sky (via Stellarium) is the approximate position that the comet will be in tonight (October 14th) at about 1-hour after sunset, if you live in the Northern Hemisphere near the 40th parallel (as I do in Salt Lake City, Utah. The appearance of the comet will be almost due west, just above the horizon, between Venus and Arcturus. You can get a more accurate prediction by going to Stellarium or using apps like PhotoPills or Planit Pro.
The comet will be a little higher in the sky each night—giving you more time to observe and photograph it before it sets below the horizon.
Here is the view I captured last Saturday night (Oct 12)—the comet's first photographable appearance in the Northern Hemisphere (prior to this date, it set below the horizon before it was dark enough to see). Astrophotographers in the Southern Hemisphere had their best shot with the comet late last month. Now it's our turn.
EXPOSURE SETTINGS: The above image was taken with a 200mm lens. If you're shooting with a normal (50mm) or wide angle lens, in order to show the comet's relationship with the surrounding landscape, try a starting exposure of f/4.0, 4 sec, ISO 800.
If you're using a telephoto lens (85mm to 200mm), try starting at f/2.8, 1.6 sec, ISO 800.
Stacking a lot of short exposures seems to work better than tracking, as the comet's path is slightly different than the rotation of the earth.
As the comet begins to set, you'll have to increase your ISO to compensate for the thicker atmosphere near the horizon that filters and dims the comet.