I'll take terms like new and oldskool just to make things easier... In my opinion there is no newskool because it is also really old stuff allready..
For one handed I don't really know, but if you have a two handed backhand open stance is the key.
(Okay, for some it isn't, and that's because they play the "old-school" way..
In my opinion; The oldschool way, you hit the ball and make a swing towards it.
try to imagine it like a line of points, where you hit the ball and take it on the line wth your racquet.
--> less spin)
New-school.. (which is as old as oldschool) you try to move your racquet in the opposite way then where you want to hit it. You only touch the ball in one point and you "smudge?" it away.
So you make a lot of spin.
In this "newschool" movement the open stance is the key.
when your legs are in close stance you simply can't move your arms and body to the other side of your body, you get blocked.
In open stance this is much easier and smoother. your arms and body can turn whole the way and there is no resistance of the body.
and also remember, if your righthanded:
The lefthand is the engine/boss; 80%
The righthand is it's helper 20%
You'll have to picture them as a mechanisme, a ?leverage?
Sorry for the english but hope you know something more now... Maybe you can put this theory on one handed backhand..
But this is why open stance is used in 2HBH