Keep high-cost moves intentional
Moving a toilet, shower or tub can trigger more work than moving a vanity. Before relocating anything, ask what problem the change solves and whether a smaller adjustment can achieve the same result.
Plan by activity zones
Think in zones: entry, toilet, grooming, bathing and storage. In shared bathrooms, separating grooming from bathing can improve usability. In an ensuite, consider sight lines from the bedroom and how much privacy the toilet area needs.
Account for real product dimensions
Nominal sizes are not enough. A vanity may have projecting hardware, a toilet may extend farther than expected, a shower door needs swing space, and trim pieces can change the finished opening. Use manufacturer drawings for the exact products being considered.
Allow for future service
Valves, pumps, floor-heat controls and other components may need access later. Avoid creating a beautiful finished surface that makes normal maintenance destructive.