I still wouldn't say that I'm really all that good at skiing switch, but the the most helpful tips for me were to stagger my feet and stay low.
Also, if you're JUST learning, I'd suggest kinda "surfing" (that's what I like to call it at least). By that I mean don't go "straight" backwards. Work slowly to that angle.
First just try 30 degrees backwards, carving heavily into the side of the mountain while still getting the feel of skiing backwards and looking over your shoulder. Then move to 45 or 60 degrees, carving a little less into the side of mountain, getting a good sense of speed while moving backwards. Everytime you need to change directions, try to do a 270 to face the other way, just to get a good feel of how to pivot.
I know those "degrees" are fucked, but if you didn't understand, read it again... it made sense to me.