Landscape photographers sometimes itch to do something a bit more artistic. When this itch strikes they sometimes move the camera while the exposure is being made with a slowish shutter speed to create some blur. At other times they may zoom while making the exposure. There are many things we can do to bring out the more artistic look. Have you tried to make the clouds move but keep the landscape steading and sharp? It is easy to do. All you need is a tripod, moving clouds, and a loooong shutter speed. Here is an example that show the effect mildly:

This technique has one obstacle; how do you get a sloooow shutter speed when your lens is already using a small F.Stop and your ISO is already set on the lowest setting AND you are still getting a shutter speed too fast for the effect you desire? Perhaps the clouds are moving too slowly and you need an even longer shutter speed. Perhaps you want to go over the top with the effect and create mega movement; as in this image below:

Here is where a neutral density filter comes in. It simply steals multiple stops of light thereby increasing your shutter speed. Since you are now using very long shutter speeds you will really need to use a tripod as I suggested. Simply install the filter and shoot. Make sure to compose and focus prior to using the filter as you may not be able to see your image on camera as it will be too dark. Shoot away. Experiment with shutter speeds to get the desired effect you want. Have fun trying this.