We've heard a few people complain that taking photos initially with their iPhone took a while to get used to because of the awkward placement of the Camera app's shutter button and the shape of the phone. Tapping the shutter button resulted in blurred or out-of-focus photos. So forget about tapping that button; we've got a better solution!
We noted that when taking photos with the iPhone it will not actually take the photo until you release the shutter button. So the key to better photography on the iPhone is to press and hold the button while you frame your shot. You can take another finger and tap the screen of an iPhone 3GS to set a focus area while still holding the shutter button down. Once you are happy, release the shutter button to take your photo.
Taking photos this way is great way to improve stabilization of the iPhone camera and your results will look a lot better.