How long is a piece of string? It all depends really, no such thing as one setting for every dusk shot. Do you have a tripod? If you do, you can leave the ISO low, in terms of shutter speed, there should be a meter you can see what shutter speed to adjust to if you want over/under/proper exposure, also depending on the aperature. Best advice is to play around with the camera. If you don't have a tripod and want to do low-light photography, go invest in one.