The Regulars, 9 x 12, oil on linen
When you read about composition in art books, you get all the usual advice about not putting a focal point smack in the middle of the canvas, dividing the canvas into thirds or fourths, the Golden Section, Fibonacci numbers, etc. Those are all good things to know, (though frankly, I don't know why the Golden Section is significant nor do I know how to apply it to my work) but not always practical.
You can crop a view so that the focal point falls on the third, but if doing so causes something else to fall where you don't want it to, it's not going to do much good. When all is said and done, designing a painting is something the artist does to communicate his intent as best he can, and you can't do that by following a formula. Composition must support the concept, and if it means tweaking value structure, colors, edges and application of paint to achieve that, then that's what we must do. In fact, tweaking is to weak a word. Design is a holistic, subjective activity, and not merely a matter of making small changes.
As I mentioned above, there are no formulas. But there are some really good practical tips about composition. Years ago I've scribbled a bunch of them on sticky notes and stuck them all over my easel to remind me. They don't necessary apply to every painting, but at the very least, they give me something to think about and design my paintings with more awareness and care.
-Unequal distribution of dark and light masses. Don't make them 50 - 50.
-Have one dominant color. Additional color masses need to be clearly lesser in visual impact.
-Use a variety of edges on every shape. Lose an edge on every shape if you can.
-Paint the concept, not things.
-Have a hierarchy of interesting areas.
-Manipulate this hierarchy with value contrast, hue choices, saturation, edges, opacity, impasto, brush activity, and textures.
-Big passive area vs. small active area
-You don't need two big passive areas.
-If the focal point is in light, simplify the shadow. If it's in shadow, simplify the light.
-If the focal point is in light, lower the key. If it's in shadow, raise the key.
-Connect shapes wherever you can. (Same thing as losing edges)
-Whenever you break a rule, make sure it looks intentional.
-Repetition and variation. Over do them. Then pull back.
-Less is more.
-Make Only One Statement!
Some of these seem not to pertain strictly to composition, but in my mind, everything affects composition. If you are clear about what you want to say with your painting (the concept), and make sure everything you do supports this concept, and nothing you put in is irrelevant, you are well on your way to designing good pictures.
Oh, and at the very top of my big studio easel, I have written in big black letters the word MYSTERY. It's a reminder for me not to put too much detail, information and identity (of the subject) into my painting. It helps me not to spell everything out for the viewer. It reminds me to paint clues, not answers, when I'm designing a picture.
I am currently waiting for the arrival of my new easel. The first thing I'm going to do is to christen it by writing MYSTERY across the top. I can't wait!