It's usually easier to start with the edge pieces - the pieces that have one or two flat sides.
Try to divide the pieces into sections, and work on those sections separately. For example, in a picture of deer standing by a wooded lake, divide the pieces into deer pieces, tree pieces, and water pieces.
Use the drawers to keep your work are uncluttered.
You can use the space bar to enlarge the target image, or to get rid of it completely in order to increase your workspace.
You can partially slide large, completed sections off the edge of the playing area in order to give yourself more work space.