As a general rule of thumb...
Point at the North Star, or the Southern Cross (unless you want a different effect than circular trails)...
Use a sturdy tripod.
Shoot film, not digital (exposures will typically be hours not seconds or minutes.
Use moderate speed film (ISO 200-400).
Use a fast lens, but close down at least one stop from wide-open to improve optical abberations at the corners of the frame.
Set the camera to T, or use B with a locking cable release.
Exposure from 20 minutes to several hours should be tried. Nights without a moon are best, but a crescent moon out of the frame may not create too much light pollution.
Needless to say, shoot from as dark a location as possible, preferably many miles from the nearest town.
Michael
