How to improve iPhone camera quality?

Well ok, I've seen people take pictures with their iPhones and the quality is crystal clear, while mine is very blurry is this an app their using or is it something else?

Lots of light. More light means faster shutter speed which reduces motion blur.

Learn how to hold your device still while taking a shot. Two hands help, and learning how to brace one, or both, arms against your body will steady your hands even more. P&S and cell phone cameras force you to hold your camera at arms length which makes for wobbly shots. Better yet, if you can bench your camera on a solid device such as a post, fence, wall, or table; you can steady your camera quite well.

I'm sorry but the quality is never "crystal clear"… At least not compared to a real camera. There's no improving phone cameras. If you want quality buy a real camera.

Could be how you are taking it (too much movement), conditions you are taking it in, the lens could be dirty, etc. Remember also the volume up button can be used as a shutter button as well.