I can't type random people or acquaintances. I type my immediate family, friends, people I date on a consistent basis, and people at work that I spend a lot of time with.
And even then after all that time spent together, I still can't type the majority of my coworkers, bosses and friends. Even if I spend years with them, I just can't figure it out. But some people are quite obvious. Depends. What I perceive first of all is whether they seem more E or I, and then I go for the T/F. Once I figure that out, because it's the easier in terms of letter, I look into the rest of it.
I focus on their two most evident functions, and go from there.
I also do a process of substraction. Instead of figuring out what functions they use, I figure out the ones that they don't (seem to) use, and by discarding you get to meat of the type, more or less. Like I figured easily that my brother in law was an ENTP because his Ne is absolutely fucking crazy. The Ne is so loud it's undeniable. So knowing that, I can start to put together the puzzle. Took me years to type him, though. And I still have friends from high school that I spent years with, and to this day I still can't tell what functions they used.