If you use the magnifying glass tool and click to zoom, it'll
zoom into the area that you click. If you select an item and use
the +/- keys on your keyboard it'll zoom into the item you have
One of the more awesome tricks I've learned though is using
the space bar. If you hold it down your cursor changes to the hand,
and you can drag your canvas around. This is true in Illustrator,
Photoshop and Flash too (probably most others as well).