I usually get a lot of ideas when I am doing something where my mind is on autopilot. That includes washing the dishes or the car, cooking, taking a bath, or taking a walk. When my mind is not engaged in what I am doing it is free to wander off to some other area and come up with ideas. Some of these ideas are worthless, but every once in a while I get a good one. So when I am doing something on autopilot I try to keep pen and paper close by (or one of my many digital devices). Try it and see if it might work for you.
What do you think?
For more ideas see this: http://www.cracked.com/blog/4-crappy-ideas-everyone-thinks-are-brilliant/