If you don't have a mouse wheel on your mouse, skip to the next page now. This is for mouse-wheel people only (although most new mice today have wheels).
While left-clicking and right-clicking can be good for zooming in and out, what if you want to zoom faster? What if you want to zoom while you have a different tool active, like the arrow tool? If you have a mouse wheel, you can zoom easily at any time.
It's simple. Point the mouse at a spot in the display, just like with the magnifying glass, but this time, instead of clicking a button, try spinning the mouse wheel. If you roll the wheel forward, you'll zoom in, and if you roll it back, you'll zoom out. Easy as pie. Go ahead and try this to get a feel for it; most advanced SpaceMonger users prefer this method for zooming.