When I begin a painting, I've already created it in my mind. The painting is complete and hanging on my wall. 
This is what imagination is. It is tapping into the universal mind, or spirit, and visualizing what already exists in essence, and then bringing it into the physical plane.
It is easy to understand this when you think of making dinner. You first think of what you want to eat. Perhaps you picture the entire meal laid out beautifully on the table, with candles and wine... you imagine if you are sharing the meal with someone... you imagine what it looks like on the table and on the plates; the smell of the food, the taste...
All of this can happen in a flash when you think, "What should I make for dinner?"
Once you know what you want to create, you get out your recipe book, head off to the store for the ingredients, and then you make dinner. Within a few hours you are enjoying your creation!
It is the same when I paint. I create an image in my mind, perhaps as an idea that I want to express.
I'll picture the size and shape of the canvas, the colours, shapes and images that will express this idea and feeling that I want to create on canvas.
I keep the finished painting in mind, but of course, there are little surprises along the way... I let go of the outcome and allow it to unfold and come to life as it is meant to.
Like giving birth - when the baby is born there is joy and surprise, yet you also feel that you knew this person all along.... everything is exactly as it is meant to be. 
Right now I have a few paintings in mind. They are there, just hanging in my mind, until I'm ready to give birth. This is the joy of creating; having a vision and then experiencing the coming into being...
