According to http://www.wikihow.com/Quickscope-in-Call-of-Duty:-Ghosts pick a weopn. the best two quickscoping sniper rifles are the L115 and the USR. If you are going to use the Sleight of hand perk, utilize the Armor Piercing attachment if you aren't going to use Sleight of Hand, utilize the Extended Mags attachment.
Also according to http://moviepilot.com/posts/2060281?lt_source=external,manual First - Practice your timing. Quick scoping is based entirely on timing and muscle memory. Practice