The trick is to line up the rail on the inrun... Look down the rail as if it's the barrel of a shotgun, and do not turn on your approach... Ski straight for the rail, using the snowplow if you need to slow down. If you can, focus on skiing straight for the end of the rail, even before you get onto it. When you take off, the rail should be directly under your crotch (let the rail go between your legs on your way up...) Keep your legs bent, twist to 90, with your feet shoulder width apart, trying to keep your hands and shoulders square with the end of the rail. Suck your knees up to meet the rail, instead of taking too much air and banging down on it. Once you get more comfortable, your hands will naturally stay at your side as you relax and grease the shiznit with style.
There is no right or wrong way to jib rails, and mileage is the best tecnique, but this method works well for me.