Use low sensitivity unless you have hidden hand perk. Hidden hand is much more noticeable with higher sensitivity. It's better to aim high than it is to aim low, aim assist will help lock onto the head that way. The best scope that I like is Shortgaze. Shortgaze is a low zoom, high aim assist scope. Best to keep moving as a sniper, don't stay hard scoped too much. If you do snipe in a snipe lane, move after a couple kills, because they're going to hunt you down when you least expect it. Snapshot and Shortgaze are a beautiful combination. Don't snipe out in the open. Utilize cover - unless you're moving and quick scoping. Memorize where your reticle will land when you scope in. Try drag scoping and twitch (flick) scoping.