So we split the problem up.
Accuracy comes from consistency of air delivery and hop, together with using decent quality BBs, the heaviest your hop will lift. There are a lot of air seal improvements you can do that don't cost anything.
Trigger response is at least partly down to motor/gearing, but at lot of it is the ability of the power system to deliver the start up current the motor needs. List the batteries, and any other information you can think of about the gun so we can start pointing you in the right direction.