Technique Summary

With a barbell on your shoulders, raise your body using your calves.  Exhale as your raise yourself, inhale on the way down.

Technique Details

As with other exercise requiring a bar on your shoulders, there are several things to note.  You could place the bar on your rear shoulder or your trapezius - whichever feels more comfortable.  You should keep an overhand grip with the thumb opposing or on the same side as your fingers.  Keeping your thumb on the same side as your fingers alleviates pressure from your wrist; keeping it on the other side provides for a more secure grip.  Keep your chest out and your back straight throughout the exercise.  Keep your feet straight, but don't lock out your knees.  Stand with your feet at shoulder width, and toes facing forward. Raise your body with your calves as far up as you can.  Breathe out as you raise your body, breathe in on the way down.

Standing with your feet flat on the floor reduces the range of motion.  You can use a foot plate (anything stable elevating your body that will allow you to stand on it with the balls of your feet) to extend the range of motion.  Usually gyms have wooden blocks that serve this purpose, or you could use one of those 4-inch aerobic steps.  At this point you should realize that keeping balance while elevated on the tips of your feet is at the very least very difficult.  This variation of this exercise should only be performed at the Smith Machine.

Since your calves are stressed every day of your life, they require higher reps and weight for development.  You should perform the exercise until you feel a burn!  The weight and the rep count will vary with your routine, but the underlying idea always remains the same - don't worry about overwhelming your calves.
Your calf consists of three muscles.  You have the medial (inside facing) and the lateral (outside facing) gastrocnemius head.  These make up the bulk of your calf.  There is also a slim muscle that extends in a line from both sides of your calf called the Soleus.  You could isolate these muscles in performing calf raises.  To isolate the lateral head (the outside facing calves) you should position your feet with toes facing in, each other.  To isolate the medial head (the inside facing calves) you need to keep your feet facing out and away from each other.  Don't over do the angle on either one.  Fifteen degrees in or our is sufficient.  To isolate the Soleus you should flex your knees.  This removes some of the pressure from the gastrocnemius to the Soleus.