Banking a Shot off of Two Rails
Count the diamonds along the long rail, starting from the one nearest the cue ball, to your intended target. This will help you bank a shot off of the short side, followed by the long side, prior to hitting your target.
Starting from the opposite side rail (the second bumper you will bank off of), count that same number of diamonds along the end rail (the first bumper you carom off of).
Aim and shoot your cue ball at the diamond you arrive at using running English, in which you strike above and to the side of its center, away from its first target. This will give it a sidespin which will cause the cue ball to rebound from an object ball or cushion at a narrower angle and at a faster speed.
Banking a Shot off of Three Rails
Plan a trajectory for the cue ball to bounce from a long rail, then a short, then the other long before hitting your intended target. Note the spot on the second long rail where the third and final bounce must occur before hitting your target.
Count the diamonds leading to it, starting from the end you make your initial shot towards, and subtract two. Count this same number of diamonds on the other long rail (the first bumper that the cue will hit) in the same direction.
Aim through and strike the cue ball into the diamond you arrive at with no English. If you use running English, add another half of a diamond to arrive at the spot you should aim at.