True to my penchant for making lists, here's a list of ways to simplify details in a landscape painting. Some are suggestions that we'll have to assume how to accomplish with blobs of paint. Others are more practical.
1. Use big brushes. "Well, duh" was my first reaction to that bit of advice. Yes, it works. However, the true detail-aholic will learn how to turn that brush every which way to suggest detail. Example: the following quick study. It's about 6"x9", done with a half-inch brush.
3. Squint. While some people recommend this for estimating values, it also works for identifying large shapes. You can use a photo editing program to blur a photo to hide those details from your detail-fiend. I love what Richard Schmid has to say about squinting in his Alla Prima book.
Non-artists watching you squint might think you are angry, in pain, or have eye trouble, but pay no attention to them because it works and that is all that counts ...Properly means closing your eyes down far enough to reduce the subject to a few shapes -- yet not so far that *all* form is lost. The idea is merely to make things simple, not make them disappear in a blur of fuzzy darks -- so don't shut your eyes down *too* far.4. Paint in values, without worrying about detail. Similar to the "paint only shapes" suggestion. Simplify everything into three or four values.
5. Leave the details to the center of interest (and do that last, so you are not tempted by detail too early).
Summary: think in shapes of color, not trees or grass. Concentrate on getting the large shapes the right value and the right color with the right edges. Gosh, that sounds so easy.
"Learning how to simplify, however, is not a simple thing." Mitchell Albala