If you're looking for the ability to walk up to a complete stranger in a close up setting, who you have no previous information on and ask them to think of someone or something, and immediately know what they're thinking, then the effect simply doesn't exist. If it did, there would be no need for swami gimmicks, centre tears, or billet switches. And if you had the power to actually read someone's mind, you probably wouldn't waste time performing simple mind reading effects. Like it's already been mentioned, if you see something like this on TV, either the pre-work hasn't been shown like in a lot of the stuff they show Blaine do, or there is some level of stooging going on (not gonna mention any TV personality names here *cough Angel *cough).
If you have 13 Steps, read through the sections on the Swami Gimmick and Billets and work on creating the illusion that you read someone's mind. Yes either you or they will have to write something down, but with the right banter and showmanship, the effect won't suffer at all.