I call my ski posture "T-Rex style" ;-)
Try starting a run by breathing out and relaxing the shoulders letting them drop, then go into your home base position with them relaxed and supported by your shoulders and core/lats. Its like punching or throwing a ball, you don't flail your arms, proper form come from the hips, core and shoulders.
Needless to say I have a lot to learn but I know this has helped me with staying forward and skiing from a more powerful position.