With landscapes, distance can be a difficult thing to capture. However if you place elements in the foreground, middle ground and in the background you will give the views eyes the ability to travel deep into the scene.
The first thing that the eye wants to do is locate the brightest spot in the scene, thereby if you place a highlight into the background we pull the eye deep into the scene right away and making the eye travel back to the foreground.

Camera specs: Canon 1-Ds Mark II with Canons EF 70 – 200mm f/2.8L IS USM lens @ 200mm, 1/200sec @ f/4.0, ISO 100, Aperture priority