Use Custom Games and play against the Bots to really get the feel for weapons. Definitely has helped me out.
I don't claim to be the most accurate, in fact my accuracy means little to me as you miss 100% of the shots you don't take.
But I have improved over the years. A lot has to do with learning maps. Know where to aim in certain situations. Where will the enemy be coming from? You'd be surprised how often pre-aiming and pre-visualizing will garner you kills.
Experiment with different setups, see what works best for you.