At low levels Deadly Aim is more so-so, you lose a fair amount of to-hit, to do extra damage to something with barely any HP.
As you level though, you'll find your accuracy improving, but critters Touch AC barely increases while their HP sky rockets.
As for general accuracy, the only thing I can recommend is Weapon Master Fighter.
Starting at level 3 they get +1 attack/damage bonuses (and every 4 after).
It also gives you the option of gaining Weapon Specialization > Point Blank Master if you don't want to spend the feats for Dodge > Mobility > Deft Shootist.
Of course, it gives you extra feats too
But PLEASE take at least 5 levels of Gunslinger before considering multi-classing.