One habit beats one tool
The leak is different in every format, so memorising what to check in a JPEG will not help you with a spreadsheet. What transfers is the habit: before any file leaves your hands, open it somewhere that shows you what is inside, and only then attach it.
Look at the whole frame, not just the subject
For anything visual, this is the step that catches the most. Notification banners, open browser tabs, a name in a corner, a document path in a title bar, a second monitor reflected in a window. No amount of metadata stripping helps with content that is in the picture.
Prefer a fresh export to an edited original
Editing a file in place preserves its history. Exporting a new one from a clean source does not. For documents that matter, finish the work, then produce a new file rather than sending the working copy.
Assume nothing about the platform
Whether a messenger or a website strips metadata depends on the app version, the platform and which upload button you pressed. Strip it yourself and the question stops mattering.