Tripod, or at least a monopod. Plus practice a lot. You need to be able to treat the camera in a relaxed, not tense, manner, even when the going gets touch and involuntary camera shake is easily introduced. VR might help, but is always a factor of unknown magnitude and importance. Don't rely solely on VR.
That being said, I sometimes am able to get very sharp images with the 300 PF at ridiculously slow speeds, in some cases down to 1/6 sec. Still I try not to do too much hand-held shooting with this lens.