Hey bro, my advice is this:
Try it alot on a box before you come anywhere near a rail with the idea of pressing it.  find flat down flats, dragons, whatever kind of box you have and dial it before you try a rail. get used to landing somewhere other than your bindings.  The big danger with pressing is you can't really get on your inside edge, so you have to worry about catching burrs and shit.  First just find a flat box and try landing on your tails, so your bindings aren't even on the box.  get as close as you can to pressing the whole thing like that, its pretty hard. then try sliding it like that.  go for a big flat rail with at least 4 feet between it and the ground so you dont catch anything if you slip off.   i'd suggest a nose press first, because it feels more natural and it'll be easier to get your hands out in front between your body and the rail if it comes to that.  just slide the rail a couple of times, make sure you disaster it cuz you're not gona be able to keep the press on any kind of kink.  get used to the rail, and then when you're sliding it one time, let your skis slide back until its just barely the toe of your binding still over the rail, overbalance forward and move you feet back more to compensate and suddenly you'll be doing a nosepress.  its super hard, and unless you're good at jibs i don't think you'll have much luck.  I can just barely do it, and it's nowhere near to the nose of my skis.  good luck though
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