The best terrain to practice this movement pattern is groomed, intermediate. The best snow condition is the grippy stuff. The stuff that's easy to carve turns in. Once you are comfortable, challenge yourself in bumps, steeps and powder. The skill focus is pressure control and the movement is absorption or retraction.
Absorption is a progressive relaxing of the outside leg at the end of the turn.
A good example of this is the movement you make when you step on a tack bare-footed. An active extension in the top half helps shape that part of the turn and pressure the ski where the forces acting on the ski and skier are relatively light. Once you've relaxed the outside leg, your base of support that counters the forces pushing you down the hill is gone and you WILL go down hill. An active extension pushes the ski into the snow allowing it to began carving before the forces in the bottom half start acting on it. In the bottom half of the turn, continue to guide the ski through the finish and flex the joints in the outside leg just enough to prevent a skid.