Turn on the Camera Grid

The iPhone camera features a grid mode that is handy for composing photos. Photographers use the rule of thirds to compose a shot and draw a viewer’s eyes to the point of focus. This setting makes it easier to line up a shot.

Turn on the grid mode to align photos better.

To turn it on open Camera -> Tap Options -> Grid to On.
The grid lines do not show up on the final photo. To learn more about how you can use this, check out this guide on the rule of thirds.