Depends on what I'm doing. Simplest would be boring spreadsheet v2.xls but there's a lot of stuff I revise a common file by a date or a course number/exam name so I will do something like assignments test #2.doc or assignments 1-17.doc.
If I am doing a home media project I will stick with the sequential version number after every major change, and usually print a video or wav file to match. With complex video you might also need scene and shot naming conventions. I learned a lot of this when I was working for a visual effects company and just ported that into my everyday workflow. When I first moved to Portland I had to create and manage a multimedia library so used those conventions.
Oh I should add the main thing is anytime something gets shared I stick a version number on it even if nobody else does, so I can track and reference changes without relying on MS tools to do it. It's also way easier to undo "fixes" other people suggest that I reject.
