Though it is often sufficient in Safari, Google Maps, etc, to double-tap in order to zoom in and out - often you need to be able to control your zooming more accurately.
The instructed method of accomplishing such is to use the two fingered "pinch" motion. Pinching your fingers together zooms the display out, while pulling your pinched fingers apart zooms the display in. We've found that this motion can often be a little clumsy, especially for those of us with iPhones that are protected by screen protectors and/or cases.
The good news is, there's an easier and more elegant way to zoom your display in and out that offers even more control than the pinching action. We've been doing it for weeks now, assuming everyone knew about it, but were suprised to find out a lot of people didn't. Here's how:Anchor one finger anywhere on the screen in a fixed position. We find the most natural way to do this is to simply let the thumb of the hand holding the iPhone slightly overlap onto the egde of the screen. Then, just drag a finger from your other on the screen to zoom in and out. Using your holding hand thumb as your anchored digit makes the zooming essentially a one finger action.