There are as many different ways to compose a painting, it often seems, as there are stars in the galaxy. Everyone seems quite sure that their way is the best way! We have your "golden sectionistas", your "sight sizers", your "Durer gridians", even your "rule of thirders" (borrowed from photography). Everyone seems to be searching for that easy way to come up with a "great" composition, every time. Then we have the "de-bunkers" who use eye tracking studies and optical science to prove why everyone else's method is a bunch of crap (excuse my English). Honestly, it's enough to make the poor itinerant artist freeze with fear each time they begin a new work.
Well folks, I'm hear to tell you that I have all of the answers and you'll never have to worry again!(Not!!) Although I love to read about all of these various methods, I have to confess, that my own method of composing a picture is quite a bit simpler. I take two L-shaped pieces of cardboard, about four inches in length, then I put them together with paper clips to form a rectangle. Some artists like to draw directly on their canvas, some like to draw on paper and then frame it out afterwards to see which size canvas to use, some like to put the canvas on the floor and wait until it looks interesting enough, with spots and stains, to generate an idea (Walter Murch actually did that!). I start with a canvas which I have traced the size onto a sheet of drawing paper. I then take my home made viewfinder and sight through it while looking at my traced rectangle and adjust it until the dimensions match. I look through my viewfinder at my setup, with one eye closed, like a pirate, it's sometimes helpful to say "arggh, shiver me timbers" while doing this. If I don't like what I see I keep adjusting things until it "feels right". Not very scientific, I know, but I have learned to trust my instincts because I have worked very hard to have them.
Another reason that I start with the traced rectangle is that I use the sides of the rectangle to mark off vertical lines so that they are parallel. Here's another "old weird dude" tip, I never use a ruler for measuring or drawing straight lines. I use a compass to mark off points and then I freehand the connecting lines. I have this idea in my head that the drawing, and subsequently the painting, would look too mechanical, too much like an architectural rendering. I remember Harold Speed in "The Practice and Science of Drawing" saying that a work of art should have a certain amount of "dithering" in it, that perfection wasn't really the goal. I'm sure he would consider me a "dithering" fool! And just to be clear, I want you to know that I'm certain that this method is truly one of the greatest lost tricks of the old masters and I'm currently working on a book with lots of diagrams to prove it. So there!