In order to "ski " correctly, you must learn where you are making your slip-ups. Most often, when a person thinks he is skiing correctly, he is actually skidding.
If you slow down when skiing, you will discover exactly where these skids are occurring. Start on flat terrain in order to move at a slower pace. Start with quarter turns making sure to dig your skis deep into the snow. Practice until you can ski a parallel turn in a full circle without skidding. As you ski and make arc shapes in the snow, for the skis to work effectively and have good edge hold throughout the whole of the arc, everything must work progressively. i.e. the leaning, steering and pressure control you make with your legs has to be skilful and precise if you want to cut a perfect arc.
If you find it difficult to increase your leg lean, then you need to find a way to gradually feel the sensations in a comfortable, achievable environment.