First lets define dropped calls, these are the calls which were picked up from your leads, but there was no available agent to take them.

The best solution for these would be to change your dial level. 

You can do that from accessing the campaign that has a lot of dropped calls. “View campaign” and click on it. 

This will open the edit menu. 

From there click on auto dial level and decrease the number. 

This will solve the dropped call percentage.