Usually one learns early in life what it takes to control the energy of others, to get them to give you energy and avoid giving your own energy away. The particular scheme used is often a reflection of which control mechanisms one's parents used.
For example, if one had a father who would always find fault in anything one said. One would probably instinctively discover that if one doesn't offer any information then there is nothing he could find fault with. You would gain power by withholding information and waiting for others to make the first move. That could easily become a permanent pattern and become a way of sucking up the energy of others in turn. If you are holding yourself back, then others will have to reach more and will enter your territory without knowing what is going on.
A control mechanism doesn't have to appear very controlling at first glance. Being meek or submissive or quiet might be a perfectly fine control mechanism. If you are submissive then people will possibly keep you around, feed you energy and rely on you.
Often a control mechanism will be a way of increasing one's status with others. It could be that one plays on being more educated, more experienced, stronger, bigger than others, or that one simply shows an arrogance that says so. High status might be gained by playing either high or low status roles. You might control others by being aloof and put them down and drive a bigger car. But a bum on the street might control others by making them feel guilt or pity. You might suck energy towards you by being unapproachable or by being overwhelming, by always staying collected, or by always starting a scene.
Control mechanisms usually fall in one of four categories, dividing people into one of four personality types:
Intimidator: Somebody who controls others by overwhelming them, commanding them, telling them what to do.
Interrogator: Somebody who gets information from others in order to find something wrong with it. Gets others to do or say something and then finds weaknesses in it.
Aloof: Somebody who doesn't volunteer information, but controls others by having them reaching for the hidden information. Stays above others by not reacting, but waiting for them to make a mistake.
Victim: Somebody who makes others feel sorry for them. Talks about and demonstrates how they are particularly unlucky or persecuted. Controls others by getting them to feel pity or guilt.
Main control mechanisms are usually somewhat hidden, even though it is something done openly. It is just that people tend not to notice. Everybody, including the person, might just assume that it is a personality trait or a natural thing to do according to the circumstances.
Having a control mechanism at all is based on the subconscious belief that there isn't enough energy to go around, that you somehow need to suck it out of others. That luckily isn't true, so it opens the door to the transformation of control mechanisms into something else.
Mainly one needs to realize what one is doing. It might be the best idea for the person to examine the phenomenon in others first, before admitting to anything personally. People tend to be kind of defensive about their control mechanisms, unless they are pinpointed very precisely. Part of the makeup of a control mechanism is to control others so as to evade being found out. If the person gets used to seeing control mechanisms in others she will tend to take her own defenses down a bit.
Examining one's early life might be a good way of identifying which control mechanism one is using. It is very likely to be a defense against something one's parents were doing as manipulation. And since that provides the proper context it is also the best place to examine the mechanism and start changing it around. Basically it was a survival response to the lack of resources in a series of incidents. It could be addressed through re-experiencing.
Any given person might use a whole number of different mechanisms and fixed ideas to be right and to control energy. However, there is most likely one or two main control mechanisms one is using continuously. Transforming those will be more valuable than any of the more peripheral ones.
A control mechanism needs to be replaced with another way of getting energy and feeling powerful, resourceful or safe. We need to find inner sources for these qualities. And we need to alleviate whatever it is that the control mechanism keeps at bay. There is some unpleasant event that it is there to keep away.