Landscapes are not limited to the traditional boroque counrtyside oil painting. A good example of a modern landscape is a cityscape. To learn more about that head over to my buildings section.
To create the most dramatic landscape, I like to include a detailed sky. Here's an example:

The Russian artist Kuindzhi (above) does a good job of using light. If you take a look you'll see that light is actually the main character of almost all of his work. We scarcely notice what is in the painting, but rather how it reflects the light. He does this by making the landscape dark and the light blinding and colorful.

If you aren't confident in your abilities, or you're just impatient, making a dark foreground with a dramatic sky is a good idea.

Just remember to avoid using lamp, jet or coal black on your silhouettes, you might get something that looks unproffesional, kind of like this, which isn't always professional.
(above: Jules Dupré)