first get fs and blindide 270s out of rails really good. Then first pop off the rail like you would do a fs 270 out but do it a lot earlier. They are really kind of easy, just focus on popping. Blindside switch ups on flats tend to be a little harder because you are... well blind. But same concept for the most part
he s talking about surface switch ups, so not leaving the rail. id say just set everything up like a normal switchup, and still pop like your body, but leave your feet down so you have hardly any weight on your skis, so they are just kinda lightly touching the rail. and put your feet close together. and when you do it wait to do most the popping and the spinning till you are really close to your skis being straight forward and backwards on the rail. so like if your doing a blindside one, start spinning first, then when your skis are just about straight on the rail, thats when you "pop" and spin 180 really fast. that way instead of popping when your skis are 90, and worrying about your skis catching for the whole 180 of the switch up, you only have like a little more than 90 degrese of the spin to worry about, and you can get the hard part (when your skis are straight with the rail) over with much faster. ive done a couple on accident just trying to do a super quick switch up, and only 1 on purpose, they are way hard. and practice on a narrow box first.
if ur spinning left try to focus on balancing on your left ski when your 50-50 and hold your feet together so u dont nut. also if your going blind side, when your backwards on the rail , lean back a little to keep your tips from hitting.