Preview size defaults to Small . Normally, GIMP uses linear interpolation. Cubic Interpolation wil take longer but sometimes yields much better results. For details on the various types of interpolation, consult a good graphics reference book. You may wish to create a new panel, add a transparent layer, and play with this option to see how these work.
Different options work better with different images.
If you are using checks instead of a solid background, you may also change the size of the checks. The undo level simply defines how many operations the GIMP remembers how to undo. This defaults to 5. If you expect to need more undo levels, make this as large as you need to, but realize that each undo level requires space to save an image state. Resize window on zoom Setting this means that zooming in on an image will cause its window to attempt to expand to contain the whole, zoomed image, and contract when images are unzoomed.