"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.
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.