Last night I went to a critique session organized by my local arts group, Fine Art League of Cary. Our expert was Bob Rankin, a well known and accomplished artist from this area. If you've never had your art critiqued in this way, I recommend you take the opportunity if it ever comes along.
We had a group of maybe 35, and 27 of us brought paintings to be critiqued, most of us having 2 pieces, so the poor guy had to go through 45 - 50 paintings in 2 hours! While it's somewhat intimidating to have your art up there under the bright lights being studied by so many pairs of eyes, the group is very supportive and Bob mixes his thoughtful and constructive criticism with a good dollop of humor that puts everyone at ease. You learn a lot not only from having your own piece analyzed but by seeing everyone else's done too.
Bob paints in various styles but is best known for his abstracts. One interesting concept he talked about (and that I had never thought about before) was the theory of edge ratios. Basically, if you look at the way the edges of your canvas are segmented by the shapes in your painting, the more uneven the segments are, the more interesting your painting will be. Here is a sketch of this idea. The short lines are where your shapes meet the canvas edge. Most artists probably do this intuitively, but it's good to have a name to give to it and know that it's an actual theory. I'll be keeping it in mind the next time I do an abstract painting!