Oops, my mistake, the question is about bank shots, not cutting frozen balls down the rails.
The rules for banking are fairly simple in my experience. Aim and hope. No seriously, never hit a bank shot too softly if you want to aim it true, I'm not sure why but when you hit them too softly the object ball will straighten off the rail and you lose the angle you played for.
It's got something to do with how the rail reacts with the object ball, it always bends slightly as the ball impacts it which effects how the ball moves away from it. Not sure of the exact physics involved though.
It's not that they can't be played softly, but doing so effects the line of the shot for banking into the pocket.
It's especially necessary to play the shot with pace if the ball is frozen against the rail and you need to make an extreme reverse cut to bank it. I'm not actually sure why, but if you hit the ball softly the ball won't bank much back towards you.
In terms of aiming them, I'm not one much for aiming systems, I do have an aiming routine though, it is as follows:
stand behind the pocket, looking at the object ball, then move to the side until behind the cue ball maintaining eye contact with the object ball while doing this. Hopefully, if you maintain eye contact with the object ball while moving from pocket to cue ball, your brain will see and remember the line that banks the object ball into the pocket.
one last thing, the rule of hitting the ball with pace while banking changes if you're trying a double bank, or a triple as I know it, i.e. banking off two rails. You need to hit this shot as softly as possible to keep the ball from reversing off the second rail. For some reason the sharp rail edges of the nine-foot style of pool table induce this effect. You can test this easily by playing a triple with pace and seeing how the object reverses off the second rail, coming back towards you.