Clean the iPhone lens
Use the rear camera
Turn off flash
Tap the moon to focus
Drag the exposure down
Use 2x, 3x, or 5x zoom if available
Avoid digital zoom as much as possible
Hold the phone steady
Use a tripod or rest the phone on a stable surface
Use a timer or the shutter delay
Turn on Night Mode only if needed
Shoot during a clear sky
Try at moonrise or moonset
Use burst mode and choose the best shot
Use a camera app with manual controls if available
Lower ISO if you can
Set a faster shutter speed if possible
Edit brightness and contrast after taking the photo