Executable images

To paint, your subject has to be EXECUTABLE...

...that is, something you can render in your chosen medium.

Lots of things LOOK good but not everything makes a good painting. It's easy to lose your head over something enticing that won't compose well, or has color issues or...any number of pit falls.
Ideally there should be discernible, eye catching contrasts. Also, some variety of color, shape, size and texture. In short, IT HAS TO BE TRANSLATABLE INTO MARKS YOU CAN MAKE, AND THE VIEWER CAN MAKE SENSE OF.
Take this example:

 It's probably a great place to canoe or hike but as a painting, mmm...not so much. The foreground, middle and distance are nearly the same value. The water, land and sky separate into bands and close areas are tangent to far areas. There's not much variety of texture either and the shapes are quite similar.
 Contrast it with this similar subject:

Now there's more variety of value between the foreground, middle and distance. The shapes are more varied, less tangential and "bite into each other", interlocking the areas. That all draws the eye THROUGH rather than ACROSS, as in the first image. There's smooth water, spiky trees, round rocks...differences you can RENDER, rather than fussily trying to adjust the micro differences of highly similar things.
 Sometimes a subject just IS "banded" or one texture abounds or the foreground, middle ground and sky are highly separated (sounds like Iowa, you say?). Here's a relentlessly horizontal subject with potentially monotonous textures.

 I've tried to counter the horizontality of the land with diagonal motion in the clouds and grass. The sky is soft, hopefully contrasting with the earth. I've "bitten" into the sky with a stem or two of grass and bitten the shadow shapes in the beans into the grass. Notice the wisp of cloud at upper left echoes the grass stem at lower right. Echoed shapes are a way to subliminally interlock areas and draw the eye from one place to another. See how many you can spot.