The types were explained to me once in a great way and it's how I type people. With some work, my brother and I have typed most of our friends. I'd say we're 70% accurate but usually come up with 1 or 2 letters that are wrong. The more you know someone, the easier it is, obviously.

E/I - How are they in social situations. Extroverts will tend to be energized by it and introverts will tend to be fatigued after a long period of socialization, needing to retire to solitude to maintain normalcy. Keep in mind that this doesn't determine how social a person is, just how they deal with socialization. I know extroverts that are very quiet and timid and introverts that are extremely outgoing and adventurous. The only thing I can say iis that introverts get worn out when they're with a lot of people and extroverts thrive.

N/S - Being intuitive, you sort of know how intuitive people work. If you're in tune with your intuition, you can recognize it in other people. Then it's just sort of an educated guess until you can scam them into taking a test. haha. I find that sensing types are usually simpler people, however, I only know extroverted Sensers. They don't tend to like talking about speculative things (quantum physics, the universe etc). They like to have plans and stick to them. This could also be attributed to the difference between Perceiving and Judging, but I'm pretty sure that it's N/S primarily.

F/T - This one is usually pretty apparent. Ts will be more plotting and can appear cold. Fs are more emotional (makes sense). This letter is in the way people talk and act. Feeling types try to make people feel better, thinking types try to make the person see why they shouldn't be mad. Ts are logic logic logic and I love and hate them for it. haha.

P/J - this is probably the most difficult letter to get right. Perceiving types take a situation and play it out in their heads, seeing more possible outcomes. Judgers take the situation as just being that way and act in it without thinking of other outcomes. It's tough to tell this one without knowing the person really well. Judging types are doers less than dreamers. Most of the judgers that I know are rather successful people, in the classic sense. They are in school, working, running some kind of volunteer work, and somehow manage to balance a caring relationship atop it all.

I think that it's also easier to type people using groups of two letters. If you learn enough about the types and read enough descriptions, you'll start to dream in Jung types. For instance, I find that most NFs act a certain way and SFs act a totally different way. TJs are vastly different from TPs.

I don't know. I feel guilty ever typing someone because it's presumptuous...but it's just so much damn fun.

Good luck, if you discover any useful info, post it please!

I have tons of visual tricks that I use. But here is the first rule of typing: Never let a person know they are being typed, many are uncomfortable with this and will lead them to hiding their Cognitive Processes.

E/I - While Nageekdoog is right about this, it can still be misleading as a person might be talking a lot and still not an Extrovert. You see this mainly is IxxJs. Watch the person's posture: are they leaning forward into the conversation or are they sitting back. An extrovert will generally not lean back unless they are in a dark place in their lives.
What are their hands doing? Introverts like to keep themselves poised, and maybe move their hands around when describing something, but they always go back to their poised positions right after. Plus you can also see and Extrovert (even if they are quiet) get more and more energized as they talk (Unless they are afraid of being hurt, or again, in a dark place.)

Ni: Watch there eyes, because perception, whether it be sensing or intuition is all in the eyes. An Ni user will do something my colleagues call the "Ni drift." When they do this, you will see they move their eyes to the upper left corner. It is kind of a dreamy like look, think JD from scrubs, it's exactly like that (Which is cool because he is an INFJ character. )This means that the person is introverting to check their Ni model for more information. Here is a video clip of Jesse Jackson (An ENFJ) using an Ni drift in a really pronounced way: He does it at 0:19 and again at about 1:01, plus other times.
http://www.youtube.com/watch?v=6H6vazOz018
Keep in mind these two things, Ni users might hide their drifts in many ways. NJs are very aware of how they look to people and my not want to be seen drifting about in mid converstation, especially the women, do to how rude it is to look like you are introverting in mid conversation. Therefore They might just drift to the lower left, or close their eyes and drift. The point is, they are going to the left, as Ni is a left brain function. Also, keep in mind that an Introvert will naturally have to drift more than an Extrovert. Also note (This is very important) that you will see eye drifts to the right as well (This is usually for right brained functions like Ti and Fi)
Oh oh oh! And don't fall into the pitfall of seeing an ISTP's and ISFP's tertiary Ni and thinking they are intuitive. They drift two, only they will not bring out as much as an INFJ for example as that process is not as strong for them.

Ne: The first thing you should notice is that Ne users bounce once their Ne get's going. Check out Milla Jovovich (an ENTP)
http://www.youtube.com/watch?v=AvoaSN9tiWw

Notice she is continuously moving except for when she has to go in and check her Ti (When she stops and looks to the right)?
Now for her eyes, an Ne types eyes to two things, "Bounce" (again) and "flash." When an Ne using type (that can be INTPs, INFPs, ENFPs, and ENTPs) are pattern surfing for possibilities their eyes sometimes bounces rapidly in different directions, Milla does that at about 1:05.
Also Ne users, specifically you ENFPs, will widen their eyes at the person they are talking to while saying something. Check out Dom DeLuise at 0:20, see that thing he did with his eyes? That is the Ne flash baby.

Ti - When person uses Ti they will probably look to the right, and drop all emotion on their face, even INFJs with Tertiary Ti do this. You can see Milla Jovovich do this, as I pointed out.

Te - You should be able to see them coming at you with extroverted judgement, but the face will be still an emotionless. Sometimes they raise their eye brows, but it is a "push" so to speak of Te. Kind of vague I know, but I want to wrap this up.

Okay I am feeling really sick and don't feel like typing anymore, I might get back to this, or you can PM if you want to know more about reading Cogitative processes in people's faces/bodies.

I use some techniques from Paul and Barbara Barron-Tieger's "Speed Typing":

1. Hands -- speaking with the hands waving, often an "E" -- especially when up at should height
2. "Smiling eyes": if the person shows a lot of emotion on the face, often someone who directs emotion outward: a TP or FJ
3. Ask about or look at their home environment: neat= J, messy = P
So from that you can have E/I_TP/FJ
4. Do they do a lot of sports? An SP
5. Into arts? Maybe an NF
6. Own expensive things? Often an NT

With those, I can get pretty close on a lot of people.

Tech. Super Tech. Epic-Godlike-Power-Tech

Also note (This is very important) that you will see eye drifts to the right as well (This is usually for right brained functions like Ti and Fi)

Yeah, I do it aaaaaaalll the time. It freaks me out sometimes, but I kinda can't stop it. LOL!