Miming is one of the great secrets of learning to have a natural technique.
The idea is really simple...
While holding the instrument you sing a passage while miming the movements of the left hand and bow arm. Feel the motions of the miming and then imitate those motions when you play normally. Repeat this exercise until your technique feels the same as the miming.
This exercise not only can work miracles technically but also helps to unlock the musical impulses of the passage.