Keep important information available
Mobile layouts should retain the main content and meaningful page information. Collapsing a section can help organization, but removing the answer because the screen is small changes the page’s purpose.
Test the awkward details
Try long headings, menus, error messages and forms with realistic input. Check for horizontal overflow and controls that crowd each other. Rotate the device and verify that zoom and keyboard interaction remain usable.
Review real tasks
Follow the same journey you would test on a larger screen, including the confirmation and the way back. Google’s mobile-first guidance is a useful technical reference, while direct usability checks show whether the experience makes sense.