Most skiers have the natural tendency of trying to force their skis to turn. 
This force can take different guises:  many people throw their shoulders
into the turn to rotate their skis, others hold their feet together and shove
out their hips, and some people even actually jump and just twist their skis in
the air.

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There is no single correct way of skiing.  As far as we know there is
not a great ski critic who sits in the sky and passes judgment on what is wrong
or right about each turn you make.  Every motion you can make has an application
in the right situation.  The way you become a really versatile skier is
learning when to apply which tactics.

In certain situations it might actually be necessary to use brute strength
and just force your skis to turn.  But these situations are rare if you
are skiing within your ability.  From beginner to expert, in all conditions,
the best tactic is to ski with grace and conserve energy whenever you can.

If you watch great skiers, one of the things that stands out about them is
how smooth they are.  Alberto Tomba does not twitch a single muscle he
does not have to, neither does Glen Plake.  Accomplished skiers move with
great power and confidence, yet flow down the hill with liquid grace. 
Here are a few secrets of smooth and powerful skiing:

Stand Naturally over your skis.  Would you walk across the room
hunched over? How much more energy does it take to stand up tall for five minutes
compared to crouching down low for the same time?  Do you walk or run with
your legs and feet held pressed together?  The answers are obvious, our
body expends less energy and functions better when we stand naturally. 
When you stand tall your skeletal structure takes up most of the weight load
of your body, the more you crouch or bend the more your muscles have to pick
up the load.  Stand tall on your skis and with your feet spread naturally
for maximum efficiency.  If the forces you create in a turn pull you down
on your skis that’s natural, you simply then return to a tall position as soon
as the forces release you.  This is a necessary response to the forces
you are experiencing, you can see this motion greatly exaggerated in top racers
due to the high forces they generate in a turn.

Add Edge Progressively:  The fundamental skill of the modern ski
turn is to be able to commit all or most of your weight to the edge of one ski,
and let the ski do as much of the work as possible.  Most skiers above
the intermediate level instinctively understand this, but most skiers also tend
to rush this motion.  You do not want to abruptly edge a ski, this is a
waste of energy, it also unbalances you, and contributes to a skidded rather
than carved turn.  At the beginning of each new turn your ski should be
flat, then you smoothly begin adding more and more edge.  As you reach
the end of a turn you begin decreasing the edge angle until you are once again
on a flat ski – ready to begin the new turn.

Add Pressure Progressively just as you are doing with the edge. 
Jamming all the weight on one ski suddenly will cause similar problems to suddenly
edging a ski. Between turns the weight should ideally be equally distributed
between both skis.  You want to smoothly add increasing pressure to the
ski at the same time you are increasing the edge angle.  Another thing
to watch is where you are pressuring your skis.  A common problem for advancing
skiers is too either lean back or forward in their boots.  If you lean
forward you are putting more pressure on the front of the ski than on the rear
of the ski, if you lean back you are doing the opposite.  Modern skis are
designed to be turned from the center, you want to distribute your weight equally
over a ski so that the entire ski is working for you.  

Move Into the Turn just as if you were riding a bicycle.  When
taking a sharp turn on a bike we naturally let our bodies bank into the turn. 
On skis you need to allow the same thing to happen.  The faster you are
going, and the sharper of a turn you are making, the further out over the snow
your body will go.  Accomplished skiers can carve such radical turns that
their shoulders are nearly brushing the snow.  If you are going slowly,
this movement still needs to happen, its just much more subtle.

The best skiers have learned how to gently apply great force.  Finesse
will get you further than pure strength will by itself, and the combination
of both leads to new heights of skiing.  The most important tool for your
skiing is a big smile, but while you are smiling strive to be fluid and efficient
with every movement – and it will just keep getting to be more fun!