As contradictory as it sounds trying to make photographs that are simple is more complicated than you would think in practice. Most people faced with landscape situations don't simply look and see things but experience an array of emotional responses triggered by their senses. We smell, we fell the cold, we hear the wind blowing but most of all our eyes see almost 180 degrees of vision. And amazingly understand it instantaneously. For a photographer to exercise the practice of making imagery simple they must first begin to see things as simple structures within the vast array of the landscape faced before them. Only then can the photographer begin to consider where to place the tripod and point the camera.
Ironically there are no simple rules to making simple photographs but the photographer must fist identify the shapes patterns and rhythms within the landscape and how they interact and position themselves within the frame of the camera. I often say it is important what you exclude from the frame as what you include in the frame. Therefore distillation is the key to simplicity's success.
When faced with all the individual elements of a landscape the photographer must train their eye to select only a small number of vital elements that into reduce structure and meaning in the photograph baring in mind at all times that simplicity is a close cousin to empty space and therefore filling the frame with all you see is a step away from this.
So next time you venture out with your camera start by choosing only three elements of the many that you feel make a good landscape photograph and do not allow any more to sneak into the composition. A difficult as it may appear at first you will slowly edge towards images with a clearer simple visual statement that mean more about you as a photographer and that the viewer can make sense of and connect with.