How do I improve my aim in CoD Blk Ops?

I suck really badly at aiming in black ops and CoD in general. i know i'm not a bad player because even with my horrible aiming i still manage a positive ratio. i know how to take cover, stratagize for different gameplay, and get the drop on people. it's just that i lose some fights i'm supposed to win due to the aim. i don't use ghost unless i'm sniping and refuse to use overpowered weapons because i don't want to depend on them to be good. i have the aim assist enabled but i've never noticed the difference. anyhelp would be appreciated. Thank You.