I usually sketch out an idea or two of a certain subject before I start to paint. The sketches I do are fairly small (these below are maybe and inch and a half wide each) and not real detailed. I don´t like to plan out my drawings in precise detail, but rather go with the main idea and then when I start on the canvas let whatever happen happen.
Here are the two sketch ideas I was working with for the painting:
As you can see the finished painting looks a bit different than the sketches.
You can see a larger view at this link.
Note I added a TV on the right hand side for the woman to rest her arm on and the second TV is in a chair - note the legs on that TV. And the perspective is a bit different than in the sketches. My initial sketches are mainly about the idea (in this case woman sitting in room by herself with TV) and then I adjust the perspective and other elements to make them a little less bland, straight on looking.
I am thinking of doing one or two other paintings probably following more closely my sketches.