Landscapes are a lot to do with depth of image. Whether that is the trees 10 metres in front of you, or the mountains 5 miles away.
Using a wide angle lens (ie 24mm or wider) the things in the background will be much smaller and having something in the foreground provides interest and draws the eye in and through the image.
Using a longer lens (say 50mm +) the eye still gets drawn in by the larger objects but by comparison objects in the distance aren't quite so small.
You also shouldn't get hung up on trying to shoot any image just because there's a foreground interest, you have to think about whether it adds to the image at all.
Just an example, shot at 17mm (full frame), it's mostly about the water around the rocks in the foreground and the coloured clouds, with the rising sun being small in the frame.
The sun will always rise by
Alistair Beavis, on Flickr
I did try different compositions, zoomed in a bit, zoomed in a lot, changing the orientation, different exposure times...
It's all about trial and error. Get out and shoot, see what works for you. Take a look at shots from other photographers and a) decide whether you like it or not then b) try to figure out why.
Then see if you can apply that to your own shots.