If you really want to get good, learn how to shoot that sucker in manual mode, ie. learn about metering, shutter speeds, and f-stops, and then set all that stuff yourself. It takes a little time but will be worth it in the end. As far as ISO goes, set it as low as possible while still keeping your shutter speed hand-holdable. Take a shot indoors with flash at ISO 100 and then at ISO 1600, zoom in and look at the difference, it should be pretty noticable. For portraits or just pics of people or anything where you really want to draw the viewer's eye to the subject, use an open f-stop (f2.8, f3.5, etc.) but make sure you focus on the subject. For lanscapes use as small a stop as possible, (f18, f22).