You have to be able to virtually read the mind of the person so that you can choose the best patterns and techniques for influencing him. Interpreting unconscious micro signs will help you with this.
Unconscious micro signs are a sort of covert form of meta communication. The person thinks of something, but he does not express it with his words. At the same time, he cannot escape his thoughts so they are projected in his actions subconsciously.
It is worth pointing out that the unconscious micro signals do not include only body language. These can come in the forms of sighs or exclamations. Throat clearing and gulping are other examples of signals which have little to do with what we define as body language.
The question is how to interpret these signals for the purposes of mindcontrol. One way is to take a book or a course. In this way, you will have the meaning of the different common signs explained to you. There is another more flexible option as well.
You have to be observant in mindcontrol in general. By paying attention, you will be able to notice these signs. You can then readily interpret them based on your own personal experience.
Just think about it. When you are touching your face, you are usually insecure and/or are thinking intensely what course of action to take. Similarly, when you are gulping, this means that you are nervous.
Once you figure out what the person is actually thinking, you can use this to make your mindcontrol even more powerful. For instance, if you notice that he is nervous, you can readily use pacing and leading to make him more relaxed.
Then you can influence him to do what you want by making relaxation and certainty some of the main benefits.