A Canvas is...
...A window. What gets painted on them is what I imagine I can see through the window.
I try to come up with a composition that works in my frame. What could you see if you were three or four feet from a window, looking out.
The branches of a cherry tree stretching across the sky. A jellyfish swimming past. A mythical portal, perhaps.
...A box. What can you fit into it?
A magic skull, or maybe a person.
Ooo this gave me some great ideas! (happy artist)
…A portal or door way. Where would you go if you had a magic portal?
I spend most of my time treating the canvas like a window. I like to take a third person viewpoint and imagine what one would see. This allows me to imagine a huge scene, but only see a small portion of it. I feel more free, knowing what is seen is not all that there is.
When imagine the canvas as a box, I feel confined and my art reflects the feeling.
Imagining the canvas as a door is similar to it being a window. The only difference is what is on the other side. Things can spill through doors once they are open.