What causes us to begin a painting or a drawing? My guess is that our answers will vary, but let's take ourselves to the times when a subject catches our attention and pulls us towards it. Chances are something will be there that's junk, not useful to the composing of the painting. On the other hand, the subject as is might need some rearranging to pull together a sound composition.
Here's a subject that got my attention a few years ago. For the first time ever, each member of my bed of bearded irises sprang forth into full bloom. One section caught my eye and pulled me towards it.
Without some selecting and placing as well as editing, it's a jumbled mess, but the way the light was striking those center flowers excited me. That brought me to five pivotal questions: What to use? What to ignore or leave out? What to emphasize? What to subdue? What to change?
Using the the rule of thirds option from the Selecting and Placing principle, I found a beginning of What to Use. Finding what to change, I spotted the flower on the upper right that I could move to the left a bit and another mid-left that I could scoot inward. And rather than use the withered blossom in front, I chose another (not in the photo) to use.
Within this rough crop, I chose to ignore the azaleas and tool building in the background, to subdue some of the textural details, to emphasize the light pattern and the shadow area of the foliage. This reinforced what caught my attention in the first place: the light.
Here's the resulting oil painting, "Irises in Light".
Asking these questions--What to use? What to ignore or leave out? What to emphasize? What to subdue? What to change?--can help us more closely scrutinize possibilities and make more aesthetically sound decisions while composing our paintings and other art works.