I don't know how to trim a hoof to setup for a shoe. But as I understand it you want the wall to be flat? Though I'm very unsure here on this cus I've never done it and that's only what I've read somewhere. Maybe someone who actually does shoeing can comment on that.
For barefoot you roll the walls. And as far as I know that's the biggest and possibly only difference.
Another thing for barefoot to be affective is to never touch the sole with a knife or rasp. ALWAYS leave the sole intact. The only time you should scrape a little sole away is in the bar/heel area to figure out how much flaky dead/compressed sole there is before you get to the living sole. This will let you know just how far down the heels need to come.
From my experience I learned so much I could on the internet from barefoot sites. I think this is a pretty good site, Bare Foot Horse
If you want to get what I consider an excellent video series that will help you learn about barefoot trimming then check out Pete Ramey's site, Pete Ramey hoof care laminitis founder horse navicular disease thrush equine foot development farrier
and get the dvd set "Under the Horse". That's how I learned. But I only trim my own horses hooves. If I had the opportunity I would learn also from an experienced barefoot trimmer. But I also think it's very worthwhile to get self educated.
Another thing that may help you learn to get some hands on experience is "find the meatwagon". Kinda gross, but learning on cadaver hooves and messing up on them is better than making big mistakes on your own horse.