Biggest thing that you can get is bevel to help with the guiding on the tunes.
Sun Valley Ski Tools is a place I recommend because they have good quality of stuff and I've just always used them and haven't had any issues. Usually I believe its typically a 1 degree bevel you put on. The more aggressive to 0 I belive is for racing. (someone correct me if I am wrong I could have this backwards)
Anyways, as far as detuning goes for edges, you want to make sure you are just down from your turning points. in most skis its the widest point that is on the tip as well as the tail of the ski. You want to shoot for just below that turning radius about an inch or so and detune there. Detune it enough to make it so that when you rub the back of your fingernail to the edge it shouldn't shave off the fingernail.
For rails typically I don't like to use a file because once you take off an edge you really can't gain it back. I'll use a detuning stone and go to town on the edge from the top of the binding to the back of it. Then I'll come back over it with a gummy stone to blend it in really well.
This is website I'd shoot for personally but you are more than welcome to pick stuff up where you like.
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