Use your phone as the organizer, not just the camera.
You usually do not need to export photos to a computer before ordering. A phone can handle the full preparation process when the final images are easy to find and you know which ones should repeat.
This guide intentionally focuses on workflow rather than detailed photo-selection advice. If you are still deciding which picture is strongest or how a square crop will look, use the separate Best Photos guide.
The simplest process is to make a shortlist, locate the original files, decide the order and duplicate pattern, then upload without repeatedly cropping or re-saving the image first.
