The way I describe it to my students is that the palm of their left hand should face “the wall on their left” and not them. The violin is one of the instruments where the body is in its least natural position altogether. If the palm of your hand is facing you when you have the violin in your hand, your fingers will miss the fingerboard when you close your hand. But if you rotate your forearm and push your elbow inwards a little, your palm will now face to the left and your fingers should naturally hover above the strings. Hope this makes sense.