A wallpaper has two jobs: it gives the phone a personal appearance and sits behind information you need to read. A photograph that looks wonderful by itself may need a different crop or a quieter Home Screen companion to work well in daily use.
Where do I add a new wallpaper?
Open Settings, choose Wallpaper and tap Add New Wallpaper. Apple’s wallpaper instructions explain choosing Photos, Photo Shuffle or another available category. Select an image, adjust the available presentation options and inspect the preview before adding it.
Pay attention to faces, text and other important details near the edge. The useful crop is the one that works behind the clock and controls, not necessarily the crop that shows the largest portion of the original picture.
Do both screens need the same picture?
No. Apple documents Set as Wallpaper Pair for using the selection across the Lock Screen and Home Screen, and Customize Home Screen for a separate treatment. The iPhone user guide also describes this choice.
Try a simpler Home Screen background if app labels and widgets become difficult to scan. A restrained colour or less detailed image can retain the mood of the photograph while making everyday navigation more comfortable.
How should I judge the result?
Lock and unlock the phone, then visit the Home Screen page you use most. Check it at your normal brightness rather than only in the editing preview. If you use a photograph containing personal information, consider what someone could see when the phone is lying on a table.
This is a new guide for the old wallpaper forum URL, with current Apple references. The final choice is personal, but a quick readability check helps the finished screen remain both attractive and useful.