i like a combination of going through the 4 dichotomies and looking at the typical picture of a certain type. i'll give an example.
my friend aaron is a social butterfly. everybody loves aaron, he's funny, smart, creative, works hard but can still be very spirit-of-the-moment. the one thing about aaron that is a bit odd is that he is also a surprisingly private guy. he has lots of friends but he'll pretty much never have a heart to heart talk with anyone.
i wanted to understand him better so i tried to find his type. i was pretty lost when i tried the dichotomies. for one thing, is he an I or an E? he's creative, but he also likes practical things, so is he an N or S? he works hard but also can be very relaxed, so is he a P or J? the one thing i was sure about him was that he's an F, just because he has so many friends and never offends anyone. it really looked like a lost cause.
however, when i read through all the characteristics of each type, it became obvious to me what type he was. ENFJ. ENFJ's out of all the E types may be the ones that NEED people the most. when they are alone, they often have very dark thoughts so the occupy themselves with friends. the FJ combination explained why he could have J characteristics and still be so relaxed and sociable.
on other occasions though, it makes perfect sense to just go through the dichotomies. it's blatantly obvious sometimes if someone's an E or I, so that's easy enough. P or J could be easy enough to understand too, especially if you're working with the guy or at school with him. you just need to see how he approaches his assignments. N or S is not too hard to distinguish if you've talked to them enough times. N types like to use analogies, comparisons and and abstract ways of describing things. S types use concrete things such as color, measurements etc. F or T? if the guy bites his tongue s no one's feelings will be hurt or likes to compliment a lot, he's probably an F. T's say what they think is right, what the truth is. i've categorized many people i think successfully using this method.
sorry for the wall of text, hope it's somewhat useful.