Snowolf is exactly right- you already know how to ride but you just need to get the feel for it.
I started out by learning basic buttering (fun!) so I could just slide back into goofy if things got too sketchy.
You pretty much learn the same way as you did for your normal stance- just take large, wide carves back and forth until you start to get the feel for it.
And yes, it really is easy to catch an edge on flat terrain! Happened to me last month when learning switch and I think I almost broke my tailbone; the pain was unbearable for a few minutes and then I had a hard time walking upstairs and couldn't do squats or situps for the rest of the week.
And that's one of the reasons I got a pair of slam shorts. They've helped for learning switch and my recent park progression.