One small tip, if you are using a tripod etc I will recomment that you switch off the VR settings in your DSLR. This is because VR doesn't work good, and is not required with Tripods.
You can try manual focus also.
For getting a proper exposure, you will need hit and trial .. Fully open aperture and change the shutter speeds .. depending on the light avaible it can vary between 1 sec to 30 sec or in a Bulb mode, practically unlimited.
[ Edit: Edited on 22-May-2013, at 06:14 by PuruS ]