When learn to ride switch on a snowboard it's just like you start over with learning how to snowboard again. So back to basic with your turns. Start really slow, sliding switch, when you wanna make a turn, remember to keep your weight on your front leg, make a good up-down movement, maybe even point your front hand in the direction you wanna go.
Even tought someone how to snowboard? Try to think up for yourself what you would say people should watch when they learn how to turn and do it yourself =P
Furthermore, I wouldn't set your board at the widest stance possible, unless you are a giant yourself. Have a width stance is really stable for railtricks, but it kills your up-down movement necessary for good turns, especially when you're still learning.
Hmm, it became a pretty long story, hope you understand tho, I always have a hard time explaining things in English