4 Use Portrait Mode
Newer iPhones (7 Plus and newer) come with Portrait Mode that uses the dual camera functionality to take better foreground pictures while blurring the background a bit. But the other good news about portrait mode is that it typically takes in more light than the traditional mode. Combine that with the good results that portrait shots can render of deeper Christmas light scenes and Christmas trees, and so it’s always a good mode to start out with when trying to get just the right shot.
On a similar note, your iPhone comes with some very good stabilization technology, but software can only do so much, especially when working with portrait mode. Even a little shaking can drastically blur all those little points of light. For the best pictures, either get a tripod or tuck in your elbows and make sure there is no movement at all when you are taking the picture.