From Carlson's Guide to Landscape Painting:.
"In many foregrounds in nature there is little to get hold of for the purposes of perspective construction, but there are always some things, such as groups of grasses, flowers, stones, depressions, cloud shadows, tree shadows, paths, roads, etc. If any of these 'materials' exist, use them to your purpose-but sparingly. Remember that the less material you use to carry conviction in a picture the better the picture will be."
Often the challenge is in exactly what to leave in, and what is extraneous.
The photograph on the left was taken just a few miles west of our home. Portions of the barn had collapsed at the time this was taken. Sadly the whole thing finally fell, and now a new "modern" barn has replaced it. Eliminating the non-essential telephone pole and street sign was an easy decision. The tree helps create depth, but in this case, I felt it was not necessary, so it too was eliminated. Left with a lot of flat negative space in the sky and ground, I added some interesting clouds from another photograph. The foreground was painted implementing some salt to create texture which, by adding interest in the foreground, gives the painting the depth needed.
Dealing with the foreground is always tricky. The tree in the foreground will immediately create a sense of depth, but it's right in the middle of the composition. I could have moved it to the left or right, but decided to eliminate it, and the remains of an old windmill. And I just use the grasses to achieve the depth.
The original photograph of this forest scene has a few elements in the foreground, such as grasses and rocks that I chose to include. Accentuating the frozen water also helps to give it depth.
Always remember that it is often more important to leave elements out of a painting to make your statement, than to try to include too much, which can often weaken a painting.