I have found this to be a lot of help for typing people in real life: Guide to typing in real time. - INTP Forum

Hope this helps.

Memorize the general preference traits. It's best to start with your own, because from there you can think about how the "opposite" preference differs from your own. Like say introvert and extrovert are the easiest. What are some of your introverted traits? Look for them in others. If you can memorize the list of traits.. run "records" on people you're trying to type.

Then get into more specific things like functions and specific type descriptions.
Hope this helped..

I found this here:
Myers-Briggs Overview | infp Blog Myers-Briggs Overview | Thoughts on the INFP Personality Type from an INFP

I/E

Here’s what I consider the two biggest indicators whether you’re an I or and E.

1. E’s easily talk to people they don’t know, and readily and naturally start conversations with strangers in public situations like standing in line a store on in an elevator, etc.

2. I’s need to recharge by having time to themselves after long social functions, even if it’s a social function they enjoy.

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N/S

My two biggest indicators of N or S preference are:

1. How a person gives directions from one place to another. S’s tend to give exact instructions, i.e. drive 4 miles south, look for the gas station on the left, turn left and go east 3 blocks. N’s give more general directions, it’s not far, drive until you see the gas station, it’s a couple blocks east.

2. N’s have a tendency to daydream. S’s don’t that often.

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F/T

Here are my biggest indicators of F or T preference:

1. F”s make impulse purchases. I’ve never known a T to just pick something up.

2. F’s have a tendency to keep knick knacks and mementos from previous relationships. T’s don’t.

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P/J

Here are my two biggest indicators on whether a person is a P or a J:

1. J’s are punctual. They show up on time. P’s are tardy or they overcompensate by showing up early.

2. J’s are methodical. They plan before they do. J’s have multiple projects but unlike P’s they finish one set of projects before they go to the next. P’s have multiple projects that have been sitting around for years.

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Hope this helps......

There is a chapter on it in this book : Amazon.com: Survival Games Personalities Play (9781450513463): Eve Delunas Ph.D.: Books.

I highly recommend the book for those interested in MBTI, even though it's based on Keirsey's system.

Well, I normally start by describing the person I'm trying to type in my head. Like are they action-oriented? Emotional? Reserved? Organized? Spontaneous? A particular trait that stands out may have something to do with their dominant function.

I find that the most reliable way to discover their type is to talk to them, rather than just observe them. If you talk to them, they may slip in something about what's going on in their minds on a regular basis.

Oh, and maybe hang around the "What's my type?" forum here on PerC. I've learned so much from reading users' posts on typing people they've never even met.

I disagree with the 'don't that often' I would say it's possibly less common, but 'don't that often' seems to be streching it a tad. Perhaps it's more visible with Ns. Or maybe replace day dreaming with zoning out. I think this is as relevant to E Vs I as it is to S Vs N.

Interesting point about the I__Js as talkative on the INTP forum.

Elessar said:

2. N’s have a tendency to daydream. S’s don’t that often.

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Haha, it's kind of nerdy but I can relate. I wish I could just give everyone the test.

I actually have guessed a few correctly, I put a lot of thought into it. I think I'm especially good an picking INFPs out because they are much like me but more sensitive, or *dreamy* types, if you will. More idealistic than me.

I can usually figure out when someone else is an NT because we have the same sort of intellect and question everything around us. INTP/J are usually obvious to me, we have the same insight and slightly bizarre/unconventional views, while being very logical and somewhat reclusive.

Otherwise, it can be hard to tell. I can usually tell when someone uses sensing over intuition because they just seem to be more, "with the program", not removed from their surroundings at all.

If someone is extremely passionate at the expense of using logic they are usually a feeler, but it's hard to tell as the functions present themselves differently depending on the situation and of course have varying degrees.

I think if I knew someone pretty well or if they were like in some ways I could type them bu otherwise it can be very difficult and surprising.