Ok ... this is my field so I'll put in my 2 cents worth (NZ cents,worth bugger all,but still)
I take a lot of shots in very dark locations,mainly the rainforest.
One thing you must have for these shots is a tripod.
I take a lot of macros of fungi and orchids,and I can only really achieve total success using the camera in manual mode.
I'm beginning to find the aperture is best set to F8 which is the cameras highest and gives best DOF
In low light conditions you're looking at anything from a 1 second to 4 second exposure,so unless you've got rocksteady hands you're going to get a blurred image.You'll need to use the timer too,because even pressing the shutter button will move the camera enough to blur the image at slower shutter speeds.
Setting the camera on program (P) is pretty much a waste of time for this kind of shot.
Using aperture priority (A) will work for some shots,but manual (M) will definitely give you the most control.
It does take practice though.
Hope this helps.
Cheers
Steve