Beside promoting your crew to veteran which provides 200% of crew ability and using manual aiming. Another tactics you can use to help in aiming accuracy is the T tactics. It's actually very famous in naval warfare. Try to broadside your ship to the front or rear of enemy ship, you will find that now you can land most of your shells on the enemy. This tactics allow the crossing line to bring all guns to bear while receiving fire from only the forward guns of the enemy. Have fun!