ASR is usually determined by two factors as what have been said by others on this forum.
Improving ASR, if ur SWITCH is showing ASR in terms of completion ratio, number of lost calls, or number of blocked calls then there is a switch problem, either your switched were not able to route traffic to its destination or interconnection congestion.
if ur subscriber werent able to finish its calls due to availablity of the network, either receives busy tones or other error tones, then you have to take a look on the performance of your switch in terms of traffic handling.