Step 1: Find a spot & start shoveling
Where ever you choose to build yours, start by digging out all the snow from the area that your quinzee will sit. Then shovel it all right back. Moving the snow like this will cause it to settle out and give your quinzee a good solid base.
Step 2: Build up a big pile of snow
Keep shoveling on snow until the base of the pile is as big as you need it to be. Once you're done, it'll look pretty conical (perhaps even comical), so feel free to use your shovels to round it into a nice dome shape.