Know what needs to change
A small visual adjustment may fit the theme's own settings. Code-level changes need a deliberate home. Write down the change and determine whether it belongs to presentation or functionality before editing a theme file.
Understand the parent relationship
A child theme inherits from its parent and provides a place for selected overrides. It can help preserve custom work when a parent theme updates, but it still needs compatibility testing. Read the parent theme's documentation before deciding which files to override.
Keep a record of customizations
Document what each change does and why it exists. Keep overrides focused and test them after an update. A smaller, understandable set of changes is easier to maintain than an entire copied parent theme.