The biggest difficulty (and fear) that people have when spinning switch is catching the edge of their outside ski on the lip (and dying). You NEED to be able to ski switch PROPERLY before you should really be attempting this, which means that you are on the same edge (and not switch-snowplowing).
Like everyone else here said, just start small - cab 1's and 3's. Look over your comfortable shoulder. LEARN how to if you aren't comfortable yet. Also, figure out which way you are most comfortable spinning switch because it can be the opposite way (I spin reg. left, switch right naturally).
Once you've got that figured out and you're comfortable, try going for a cab 5 (considering that it's the first true switch spin....because cab 1's and 3's you are never blind). You'll want to set your rotation with a good swing of the arm in your spinning direction (at least at first to get used to the rotation) and KEEP looking to where you want to do.
One of the most important things is having patience when taking off - wait until your feet reach the lip before you pop and start your rotation. Starting your spin too early will most likely result in you catching your edge/getting a shitty rotation/dying.
Once you've waited for a good pop and gotten yourself around, spot your landing and stomp it. It'll take a few tries to get used to it, but once you have it on lock it's probably one of the easiest tricks you can do. Work on getting grabs in there, and then when you're feeling good just experiment with different levels of throwing yourself for cab 7/9/10 etc etc...
And most importantly.....practice. You'll probably just need to man up (at first) and say "fuck it".
Good luck.
