You must spend hours with a person, getting to know them, learning how they interact with other people, how they process information, and even how they smile. Once you've got all the nuances down, you can start to ask them questions, and judge the way they react, ponder, and answer. Eventually you'll want to sleep next to them, to get a feel for how their mind works - for the human mind relaxes and opens up during the sleep cycle. Sex is also very helpful, but not always practical.
Think of it as learning another language, completely from scratch to fluency, with each new person that you wish to read. Only when you've mastered the language do you hope to be able to hold complex conversations with a native speaker, and only when you've mastered another person's mind can you attempt to read it.
And you must be in very close proximity to the person you're attempting to read. Touching is best, but when sitting within arms length it's possible.
With enough practice, and a lot of finger crossing, you can literally transport your psychic essence into the other person's brain, and reside there along with their psychic essence. You can share their body.
You can't control them. Or at least, I can't. I've spoken with at least two other telepaths who claim to be able to either influence the actions of their host, or directly affect them. I've never managed it though.
While in another person's mind, you are privy to their thoughts, their wishes, their daydreams, and their nightmares.
You don't have to know a person to read their minds or transport into their body. You can get there by reading things they've written. You can get inside the mind of a very good author, provided that he's written diversified and numerous volumes.
The key is that you should read things that the author has poured his heart and soul into. Journals and diaries are gold. A philosophical writer is easiest, a novelist isn't too hard either. A person who writes textbooks is virtually impossible.
And here we come to the point of this jumble of words on page: What if the person whose writings you're reading is dead? Why then, you can transport into their mind at a random point before their death. Most often at the time that they wrote the last thing that you read.
I have a collegue who delved into Anne Frank's diary, transported, and came back shaking. He didn't stop shaking for a week, and refuses to talk about what he experienced.
Another collegue decided to try Hitler, with the hopes of influencing his actions and stopping the Holocaust. He never came back. My only conclusion is that Hitler, with his very strong will, sensed my friend and either killed his spirit or trapped him within his own mind.
I talk of transporting and coming back. Let me explain how it's done. It's hard to explain, easier to show. Thus, I stand little chance of conveying my meaning to you on page, but I'll do my best.
When you've acquired enough of a person's essence to attempt to go into their mind, you lay down and concentrate with all of your will upon that person. If all is in order, eventually you will pass into a trance (easily mistaken for a coma) and seem to 'awaken' within that person's mind. You are a visitor only, you cannot control the host body.
You have all five senses - you can see out of your host's eyes, hear with their ears, taste what they eat or drink, smell the air they breathe, and feel what they touch. You can read their mind in this state, and sometimes, if you concentrate enough, force your thoughts into their brains.
Have you ever had a sudden thought, quite unlike yourself? A feeling that you should do something, but you don't know why? That is what it is like - perhaps you've even had a telepath in your mind at one point.
I have yet to meet anyone who has actually, literally, communicated with their host. As far as I know, no host (who was unaware of the attempt to enter their mind) has ever realized that they were indeed a host for another conciousness. Except, peryhaps, for Hitler.
When you're in another's mind, your mundane body appears to be in a coma. Without medical attention, you can only visit for 3 days, before needing to return to your body to take nourishment. However, the Institute has a doctor on staff who will supply liquids and nutrients via IV to anyone who requests it. This way, we can remain in stasis indefinatly.
Attempting to connect is extremely difficult. You fail 90% of the time, and must rest between attempts. Mindwork is a grueling exercise.