Have a look at this classic clip from Spa Cycles.
[media]
]View: https://www.youtube.com/watch?v=-XUFVrl0UT4[/media]
There's some pretty good advice that's useful for tyres that are not Marathon Pluses.
He is wrong, think what starting from the valve does, tip it gives you less tyre to work with. The valve keeps the tyre from dropping into the well.