iso: lowest iso possible (e.g. 100/200).
aperture : f/3.5 (use widest aperture).
shutter speed : BULB.
WB : auto.
Focus : manual focus (use infinity).
a shutter release cable / remote.
stop watch to record how many minute you are aimming for.
Make sure you are aimming at a dark area. no lights at the focus distances, (you're picture will be overexposed or burst).
After you have release you shutter, don't be worry if there are no picture in your moniter, this due to the camera is processing your picture (please DON'T turn off your camera, untill the picture you've taken has turn out in your view monitor). It will take at least if you take the picture for 5mins the process with take up to 10mins.
HAVE A NICE TRY.... ENJOY.