Skiing puts you into a pretty uncomfortable and awkward position if you aren't used to it. The boots push you forward, but the weight of the front of your skis scoots you back. Many beginners will either lean way back (often referred to as back-seat skiing) or way forward to counter-balance themselves. This is wrong. Keeping your legs squarely under your torso with your shoulders pointing downhill will give you a stronger technique with more control. Keeping your body weight directly over the ski's narrowest point (the sweet spot) will have the ski work for you, not against you.
Editor's Hint: If your feet are in front of your body, your leg muscles will have to work overtime to start your next turn. Skiing out of balance is exhausting. Skiing in balance is effortless.