Help with rails?...

well if you need to stop to do a front 270 out grip and rip

force your edge into the edge of the rail or box, angled if you want to switch up, spin off, ect.

You essentially use your edges to help you shift your weight. So lets just say you slide right foot forward you would use your right foot to put pressure on the edge so that you stop yourself. So if your coming up to a rail you would jump on ( right foot forward assuming ) and take your front foot and raise your tip of the ski up so that your edge is on the edge of the rail and with that you can stop your rotation.

pretty much it...it takes a little while to get used to, but just keep practicing 270 on to boxes and try and stop yourself and try and land out switch. Or, if your box is wide enough and long enough just get on and spin then try and spin the other way before the end - it'll really help you get used to it, even if you don't end up spinning the other way (that's not really the point anyways).

stop looking around with your head and shoulders.

grip with the ski that is going down the mountain, to go front side lift toes up, to do blind side put toes down