I actually shoot at a relatively low ISO. I just stay very still and hope that the model can hold her pose as well. I never shoot at anything above 800 ISO. Really, one of the secrets is the camera. Nikon really handles low light incredibly well, @patschwork.

Thanks a lot for your answer. I´m sometimes struggeling with my Canon and I think it doesn´t handle that as well as the Nikon.. At least my models have no problems standing still :)