IMO there are two pre-shot routines, the first is while you are standing behind the ball deciding on your shot. This can be all in the mind, but having some physical "cues" can be good as well. On the mental side you should get in the habit of always deciding
1. where you will hit the object ball.
2. where you will hit the cueball (follow, draw, spin)
3. how hard you will strike the shot
4. a reasonable idea of where the cuball will stop
This sounds simple, and something everyone knows we should already be doing. But if you pay attention you may be surprised to find out how many times you are down in your stance and still making these choices.
A physical cue can be as simple as setting down the chaulk, just some move that you always do to tell your body you are ready to take your stance.
Some people are very good at the first routine, standing the same way behind the shot each time and going through the proper motions. But the second preshot routine is as important, if not more, than the first.
The second routine is as you are down on the shot, taking the same amount of warm up strokes before you hit the shot. In the "set, pause, finish, freeze" teaching this is what is known as the set. Please understand that if your routine is 3 strokes, pause, and then hit the shot, this doesnt mean that once you are down you can only take 3 warm up strokes.
For instance, if you get down, take three warm up strokes, look at your target and feel you need to adjust, by all means adjust. Then start the 3 strokes over again. The pause is what gives your mind time to decide if you are really ready to strike the shot. But it should become second nature that before actually hitting the cueball you always take the same "set" in the same way before each shot.
Most people will take 1 to 5 strokes as their set, this is something you will have to experiment with to find what works best for you. But once you have found it, practice it untill you no longer think about it.
I hope this helps you in some way, I am sure many will come behind me with some great suggestions.
Woody