You can take a photo in the Camera app by pressing either of the volume buttons on the inline remote on the iPhone’s headphones. This allows you to keep the iPhone steady as you don’t need to touch it. This can be particularly useful when using a tripod or leaning your device against a surface. It works wonders for initiating Time-Lapse mode.
If you have a Bluetooth headset connected, you can also press the Volume Up or Down buttons on it to take the photo remotely. Now you can get the perfect group shot.