Follow three simple rules:
1. Line the perpendicular from the Origin Point to the rail to bank upon
2. Find the similar perpendicular line from the Destination Point to the same rail
3. Drop a third parallel line from the cross point to the rail
The red dashed arrow indicates where the bank needs to be hit to score. We are ignoring less than perfect rails on worn tables, hitting harder or softer than a medium speed and applied english, any of which would alter the path of the bank somewhat.
However, for any bank or kick taken off one cushion, this three step principle dividing the "square" will always apply.