Here's a very common system for banking that I learned a few years back. This system basically calculates the exact point on the cushion to aim the object ball. Refer to the illustration below.
Draw a line from the middle of the object ball into the cushion which is parallel to the opposite end of the table (line A). Next, draw a line from the point on the cushion pointed to by line A and into the pocket where you plan to pocket the object ball (line B). Next, draw another line from the middle of the object ball into the opposite side pocket (line C). From these three lines, find the point where line B and line C intersects and draw a line from that point into the cushion parallel to line A (white line in the illustration above). The point at which this line hits the cushion is where you should aim the object ball to hit in order for it to go into the pocket.
Keep in mind that the system explained should be used with center ball hit on the cue ball with the right amount of speed. This will be similar to the "Angle In" equals "Angle Out" theory. Also bear in mind that you should use this system only as a guide whenever you have difficulty calculating the exact point of aim on the cushion. After executing several bank shots, you should be able to be familiar with where to aim the object ball by feel.
