Holding a Leica is no different from other cameras - you're taught to support the bottom of the camera with your left hand, cradling the lens (which is preferred) but in the picture above you see an alternative method which allows rapid portrait or landscape orientations. You also want to brace yourself as much as possible; arms tucked in, knees relaxed with feet spread a bit. If you have to, don't be afraid to use anything and everything around you for additional support; lean against a wall, etc. You can also lay your camera atop a bag or jacket and use the self timer to your advantage, even without a tripod or cable release.