Personally, i hold my breath a little bit whilst zooming in. I find it makes it more accurate, and you're more likely to hit the target because of reduced sway.
Hold L1 for about half a second, then hold L3 simultaneously. Then shoot, obviously.
360's aren't too hard either with practice, eventually you'll mentally know how long it takes to do a full spin with the sensitivity that you're on. This works for 720's, 1080's etc
No-Scoping really is all luck tbh, don't listen to all these bullshit techniques on how to do it properly.
You're more likely to hit the targer if you're laying down, as the cross heirs are smaller, (Same with crouching).
Eventually you can go into Ghostying/throwing knife trick. But cba to go into that now, just ask and i'll explain it to you
+Rep if i helped