The rule of thirds suggest you put your horizon line a third from the bottom or a third from the top of your frame. The horizon needs to be straight.
The rock in the foreground is the "foreground interest" I think all landscape shots of this type should have. Foreground interest help creating depth.
The best landscape shots are taken at sunset or at dawn, to capture the low sun. A low sun adds a warmer tone to your picture. A sky with some clouds create more interest than a clear sky. Stay around after sunset, some of the best shots are taken up to half an hour after sunset.
A video tutorial on composition can be found here.