i learned my noscoping in cs:s by playing lots of scoutzknivez against people that were ridiculously good… i never had time to scope in and set up a shot, by then i was dead, so i got used to just laying out “cover fire” noscoping… nowhere near as effective as in any other game, as they can very well still stay aimed straight on through impact, but it keeps them out of the doors sometimes… but then like they be sayin i got a feel for where it’d hit. if you want some practice, start a one-man server of your own just over LAN and use the crosshair spray and tag a wall at the end of a long runway and noscope at it while running, crouching, standing, walking, etc… or just go ballsy and try noscoping through a great many deaths and you’ll catch on 
and for me, even at my best, noscoping the scout was 50% skill and 50% pure dumb luck… but it’s better than my chances of not getting shot while i’m setting up a proper scoped shot, so you won’t catch me scoping.
on occasion, I’ll grab an awp off a corpse that I just knifed… just for lulz… if i’m behind the whole other team then i’ll stop and scope in, but otherwise i try to noscope it and i’m still terrible. i can’t even hit them anywhere…